30.1: Introduction

The structures of animals consist of primary tissues that make up more complex organs and organ systems. Homeostasis allows an animal to maintain a balance between its internal and external environments.

Homeostasis describes the dynamic balance of the body’s internal environment and the effort to maintain a constant, stable inside. There are many body components that contribute to homeostasis. Animals use homeostatic mechanisms to regulate things like pH, water and ion content, body temperature, blood pressure, and blood glucose. Not all animal bodies regulate all of these examples.

Animals vary in form and function. From a sponge to a worm to a goat, an organism has a distinct body plan that limits its size and shape. Animals’ bodies have evolved to interact with their environments, whether in the deep sea, a rainforest canopy, or the desert. Therefore, a large amount of information about the structure of an organism's body (anatomy) and the function of its cells, tissues and organs (physiology) can be learned by studying that organism's environment.

In lab we will be dissecting several animals in order to compare their anatomy and physiology. We will dissect a squid (mollusc), a frog (amphibian), a pigeon (bird), and a rat (mammal). The structure of an organism's body (anatomy) largely determines and limits the functionality (physiology) of that body. As you dissect animals in our lab, focus on the structures you are encountering and how they determine function. Consider what the role of that structure is in relation to other organs and how structures are put together into body systems.

We will see components and discuss functionality of the following systems:

1. Integumentary System
2. Musculoskeletal System
3. Digestive System
4. Circulatory System
5. Respiratory System
6. Nervous and Sensory Systems
7. Reproductive and Endocrine Systems
8. Osmoregulatory System

1. Integumentary System:

The integumentary system includes all coverings of the animal body. As you dissect animals in lab notice the different kinds of skin and integument and the structures that are derivatives of this system (hair and hair follicles, whiskers, bumps, horns, etc.).

2. Musculoskeletal System:

Muscle cells are specialized for contraction. Muscles allow for motions such as walking, and they also facilitate bodily processes such as respiration and digestion. The body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Recall the differences in these three muscle types that you saw under the microscope.

Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal muscle also has multiple nuclei present in a single cell.

Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per cell, is tapered at both ends, and is called involuntary muscle.

Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure. Like skeletal muscle, cardiac muscle is striated, but unlike skeletal muscle, cardiac muscle cannot be consciously controlled and is called involuntary muscle. It has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disks.

A skeletal system is necessary to support the body, protect internal organs, and allow for the movement of an organism. There are three different skeleton designs that fulfill these functions: hydrostatic skeleton, exoskeleton, and endoskeleton.

Hydrostatic Skeleton

A hydrostatic skeleton is a skeleton formed by a fluid-filled compartment within the body, called the coelom. The organs of the coelom are supported by the aqueous fluid, which also resists external compression. This compartment is under hydrostatic pressure because of the fluid and supports the other organs of the organism. This type of skeletal system is found in soft-bodied animals such as sea anemones, earthworms, Cnidaria, and other invertebrates.

Exoskeleton

An exoskeleton is an external skeleton that consists of a hard encasement on the surface of an organism. For example, the shells of crabs and insects are exoskeletons. This skeleton type provides defence against predators, supports the body, and allows for movement through the contraction of attached muscles. As with vertebrates, muscles must cross a joint inside the exoskeleton. Shortening of the muscle changes the relationship of the two segments of the exoskeleton. Arthropods such as crabs and lobsters have exoskeletons that consist of 30–50 percent chitin, a polysaccharide derivative of glucose that is a strong but flexible material. Chitin is secreted by the epidermal cells. The exoskeleton is further strengthened by the addition of calcium carbonate in organisms such as the lobster. Because the exoskeleton is acellular, arthropods must periodically shed their exoskeletons because the exoskeleton does not grow as the organism grows.

Endoskeleton

An endoskeleton is a skeleton that consists of hard, mineralized structures located within the soft tissue of organisms. An example of a primitive endoskeletal structure is the spicules of sponges. The bones of vertebrates are composed of tissues, whereas sponges have no true tissues. Endoskeletons provide support for the body, protect internal organs, and allow for movement through contraction of muscles attached to the skeleton.

The human skeleton is an endoskeleton that consists of 206 bones in the adult. It has five main functions: providing support to the body, storing minerals and lipids, producing blood cells, protecting internal organs, and allowing for movement. The skeletal system in vertebrates is divided into the axial skeleton (which consists of the skull, vertebral column, and rib cage), and the appendicular skeleton (which consists of the shoulders, limb bones, the pectoral girdle, and the pelvic girdle).

3. Digestive System:

Animals obtain their nutrition from the consumption of other organisms. Depending on their diet, animals can be classified into the following categories: plant eaters (herbivores), meat eaters (carnivores), and those that eat both plants and animals (omnivores). The nutrients and macromolecules present in food are not immediately accessible to the cells. There are a number of processes that modify food within the animal body in order to make the nutrients and organic molecules accessible for cellular function. As animals evolved in complexity of form and function, their digestive systems have also evolved to accommodate their various dietary needs.

Herbivores, Omnivores, and Carnivores

Herbivores are animals whose primary food source is plant-based. Examples of herbivores include vertebrates like deer, koalas, and some bird species, as well as invertebrates such as crickets and caterpillars. These animals have evolved digestive systems capable of handling large amounts of plant material. Herbivores can be further classified into frugivores (fruit-eaters), granivores (seed eaters), nectivores (nectar feeders), and folivores (leaf eaters).

Carnivores are animals that eat other animals. The word carnivore is derived from Latin and literally means “meat eater.” Wild cats such as lions and tigers are examples of vertebrate carnivores, as are snakes and sharks, while invertebrate carnivores include sea stars, spiders, and ladybugs. Obligate carnivores are those that rely entirely on animal flesh to obtain their nutrients; examples of obligate carnivores are members of the cat family, such as lions and cheetahs. Facultative carnivores are those that also eat non-animal food in addition to animal food. Note that there is no clear line that differentiates facultative carnivores from omnivores; dogs would be considered facultative carnivores.

Omnivores are animals that eat both plant- and animal-derived food. In Latin, omnivore means to eat everything. Humans, bears, and chickens are example of vertebrate omnivores; invertebrate omnivores include cockroaches and crayfish.

Invertebrate Digestive Systems

Animals have evolved different types of digestive systems to aid in the digestion of the different foods they consume. The simplest example is that of a gastrovascular cavity and is found in organisms with only one opening for digestion. Platyhelminthes (flatworms), Ctenophora (comb jellies), and Cnidaria (coral, jelly fish, and sea anemones) use this type of digestion. Gastrovascular cavities are typically a blind tube or cavity with only one opening, the “mouth”, which also serves as an “anus”. Ingested material enters the mouth and passes through a hollow, tubular cavity. Cells within the cavity secrete digestive enzymes that break down the food. The food particles are engulfed by the cells lining the gastrovascular cavity.

The alimentary canal is a more advanced system: it consists of one tube with a mouth at one end and an anus at the other. Earthworms are an example of an animal with an alimentary canal. Once the food is ingested through the mouth, it passes through the esophagus and is stored in an organ called the crop; then it passes into the gizzard where it is churned and digested. From the gizzard, the food passes through the intestine, the nutrients are absorbed, and the waste is eliminated as feces, called castings, through the anus.

Vertebrate Digestive Systems

Vertebrates have evolved more complex digestive systems to adapt to their dietary needs. Some animals have a single stomach, while others have multi-chambered stomachs. Birds have developed a digestive system adapted to eating unmasticated food.

Monogastric: Single-chambered Stomach

As the word monogastric suggests, this type of digestive system consists of one (“mono”) stomach chamber (“gastric”). Humans and many animals have a monogastric digestive system. The process of digestion begins with the mouth and the intake of food. The teeth play an important role in masticating (chewing) or physically breaking down food into smaller particles. The enzymes present in saliva also begin to chemically break down food. The esophagus is a long tube that connects the mouth to the stomach. Using peristalsis, or wave-like smooth muscle contractions, the muscles of the esophagus push the food towards the stomach. In order to speed up the actions of enzymes in the stomach, the stomach is an extremely acidic environment, with a pH between 1.5 and 2.5. The gastric juices, which include enzymes in the stomach, act on the food particles and continue the process of digestion. Further breakdown of food takes place in the small intestine where enzymes produced by the liver, the small intestine, and the pancreas continue the process of digestion. The nutrients are absorbed into the blood stream across the epithelial cells lining the walls of the small intestines. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces; it is stored until it is excreted through the rectum.

Avian

Birds face special challenges when it comes to obtaining nutrition from food. They do not have teeth and so their digestive system must be able to process un-masticated food. Birds have evolved a variety of beak types that reflect the vast variety in their diet, ranging from seeds and insects to fruits and nuts. Because most birds fly, their metabolic rates are high in order to efficiently process food and keep their body weight low. The stomach of birds has two chambers: the proventriculus, where gastric juices are produced to digest the food before it enters the stomach, and the gizzard, where the food is stored, soaked, and mechanically ground. The undigested material forms food pellets that are sometimes regurgitated. Most of the chemical digestion and absorption happens in the intestine and the waste is excreted through the cloaca.

Parts of the Digestive System

The vertebrate digestive system is designed to facilitate the transformation of food matter into the nutrient components that sustain organisms.

Oral Cavity

The oral cavity, or mouth, is the point of entry of food into the digestive system. The food consumed is broken into smaller particles by mastication, the chewing action of the teeth. All mammals have teeth and can chew their food.

The extensive chemical process of digestion begins in the mouth. As food is being chewed, saliva, produced by the salivary glands, mixes with the food. Saliva is a watery substance produced in the mouths of many animals. There are three major glands that secrete saliva—the parotid, the submandibular, and the sublingual. Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains immunoglobulins and lysozymes, which have antibacterial action to reduce tooth decay by inhibiting growth of some bacteria. Saliva also contains an enzyme called salivary amylase that begins the process of converting starches in the food into a disaccharide called maltose. Another enzyme called lipase is produced by the cells in the tongue. Lipases are a class of enzymes that can break down triglycerides. The lingual lipase begins the breakdown of fat components in the food. The chewing and wetting action provided by the teeth and saliva prepare the food into a mass called the bolus for swallowing. The tongue helps in swallowing—moving the bolus from the mouth into the pharynx. The pharynx opens to two passageways: the trachea, which leads to the lungs, and the esophagus, which leads to the stomach. The trachea has an opening called the glottis, which is covered by a cartilaginous flap called the epiglottis. When swallowing, the epiglottis closes the glottis and food passes into the esophagus and not the trachea. This arrangement allows food to be kept out of the trachea.

Esophagus

The esophagus is a tubular organ that connects the mouth to the stomach. The chewed and softened food passes through the esophagus after being swallowed. The smooth muscles of the esophagus undergo a series of wave like movements called peristalsis that push the food toward the stomach. The peristalsis wave is unidirectional—it moves food from the mouth to the stomach, and reverse movement is not possible. The peristaltic movement of the esophagus is an involuntary reflex; it takes place in response to the act of swallowing.

A ring-like muscle called a sphincter forms valves in the digestive system. The gastro-esophageal sphincter is located at the stomach end of the esophagus. In response to swallowing and the pressure exerted by the bolus of food, this sphincter opens, and the bolus enters the stomach. When there is no swallowing action, this sphincter is shut and prevents the contents of the stomach from traveling up the esophagus. Many animals have a true sphincter; however, in humans, there is no true sphincter, but the esophagus remains closed when there is no swallowing action. Acid reflux or “heartburn” occurs when the acidic digestive juices escape into the esophagus.

Stomach

A large part of digestion occurs in the stomach. The stomach is a saclike organ that secretes gastric digestive juices. The pH in the stomach is between 1.5 and 2.5. This highly acidic environment is required for the chemical breakdown of food and the extraction of nutrients. When empty, the stomach is a rather small organ; however, it can expand to up to 20 times its resting size when filled with food. This characteristic is particularly useful for animals that need to eat when food is available.

The stomach is also the major site for protein digestion in animals other than ruminants. Protein digestion is mediated by an enzyme called pepsin in the stomach chamber. Pepsin is secreted by the chief cells in the stomach in an inactive form called pepsinogen. Pepsin breaks peptide bonds and cleaves proteins into smaller polypeptides; it also helps activate more pepsinogen, starting a positive feedback mechanism that generates more pepsin. Another cell type—parietal cells—secrete hydrogen and chloride ions, which combine in the lumen to form hydrochloric acid, the primary acidic component of the stomach juices. Hydrochloric acid helps to convert the inactive pepsinogen to pepsin. The highly acidic environment also kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the hydrolysis of protein in the food. Chemical digestion is facilitated by the churning action of the stomach. Contraction and relaxation of smooth muscles mixes the stomach contents about every 20 minutes. The partially digested food and gastric juice mixture is called chyme. Chyme passes from the stomach to the small intestine. Further protein digestion takes place in the small intestine. Gastric emptying occurs within two to six hours after a meal. Only a small amount of chyme is released into the small intestine at a time. The movement of chyme from the stomach into the small intestine is regulated by the pyloric sphincter.

When digesting protein and some fats, the stomach lining must be protected from getting digested by pepsin. There are two points to consider when describing how the stomach lining is protected. First, as previously mentioned, the enzyme pepsin is synthesized in the inactive form. This protects the chief cells, because pepsinogen does not have the same enzyme functionality of pepsin. Second, the stomach has a thick mucus lining that protects the underlying tissue from the action of the digestive juices. When this mucus lining is ruptured, ulcers can form in the stomach. Ulcers are open wounds in or on an organ caused by bacteria (Helicobacter pylori) when the mucus lining is ruptured and fails to reform.

Small Intestine

Chyme moves from the stomach to the small intestine. The small intestine is the organ where the digestion of protein, fats, and carbohydrates is completed. The small intestine is a long tube-like organ with a highly folded surface containing finger-like projections called the villi. The apical surface of each villus has many microscopic projections called microvilli. These structures are lined with epithelial cells on the luminal side and allow for the nutrients to be absorbed from the digested food and absorbed into the blood stream on the other side. The villi and microvilli, with their many folds, increase the surface area of the intestine and increase absorption efficiency of the nutrients. Absorbed nutrients in the blood are carried into the hepatic portal vein, which leads to the liver. There, the liver regulates the distribution of nutrients to the rest of the body and removes toxic substances, including drugs, alcohol, and some pathogens.

The human small intestine is over 6m long and is divided into three parts: the duodenum, the jejunum, and the ileum. The “C-shaped,” fixed part of the small intestine is called the duodenum. The duodenum is separated from the stomach by the pyloric sphincter which opens to allow chyme to move from the stomach to the duodenum. In the duodenum, chyme is mixed with pancreatic juices in an alkaline solution rich in bicarbonate that neutralizes the acidity of chyme and acts as a buffer. Pancreatic juices also contain several digestive enzymes. Digestive juices from the pancreas, liver, and gallbladder, as well as from gland cells of the intestinal wall itself, enter the duodenum. Bile is produced in the liver and stored and concentrated in the gallbladder. Bile contains bile salts which emulsify lipids while the pancreas produces enzymes that catabolize starches, disaccharides, proteins, and fats. These digestive juices break down the food particles in the chyme into glucose, triglycerides, and amino acids. Some chemical digestion of food takes place in the duodenum. Absorption of fatty acids also takes place in the duodenum.

The second part of the small intestine is called the jejunum. Here, hydrolysis of nutrients is continued while most of the carbohydrates and amino acids are absorbed through the intestinal lining. The bulk of chemical digestion and nutrient absorption occurs in the jejunum.

The ileum is the last part of the small intestine and here the bile salts and vitamins are absorbed into blood stream. The undigested food is sent to the colon from the ileum via peristaltic movements of the muscle. The ileum ends and the large intestine begins at the ileocecal valve. The vermiform, “worm-like,” appendix is located at the ileocecal valve. The appendix of humans secretes no enzymes and has an insignificant role in immunity.

Large Intestine

The large intestine reabsorbs the water from the undigested food material and processes the waste material. The human large intestine is much smaller in length compared to the small intestine but larger in diameter. It has three parts: the cecum, the colon, and the rectum. The cecum joins the ileum to the colon and is the receiving pouch for the waste matter. The colon is home to many bacteria or “intestinal flora” that aid in the digestive processes. The colon can be divided into four regions, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. The main functions of the colon are to extract the water and mineral salts from undigested food, and to store waste material. Carnivorous mammals have a shorter large intestine compared to herbivorous mammals due to their diet.

Rectum and Anus

The rectum is the terminal end of the large intestine. The primary role of the rectum is to store the feces until defecation. The feces are propelled using peristaltic movements during elimination. The anus is an opening at the far-end of the digestive tract and is the exit point for the waste material. Two sphincters between the rectum and anus control elimination: the inner sphincter is involuntary and the outer sphincter is voluntary.

Accessory Organs

The organs discussed above are the organs of the digestive tract through which food passes. Accessory organs are organs that add secretions (enzymes) that catabolize food into nutrients. Accessory organs include salivary glands, the liver, the pancreas, and the gallbladder. The liver, pancreas, and gallbladder are regulated by hormones in response to the food consumed.

The liver is the largest internal organ in humans and it plays a very important role in digestion of fats and detoxifying blood. The liver produces bile, a digestive juice that is required for the breakdown of fatty components of the food in the duodenum. The liver also processes the vitamins and fats and synthesizes many plasma proteins.

The pancreas is another important gland that secretes digestive juices. The chyme produced from the stomach is highly acidic in nature; the pancreatic juices contain high levels of bicarbonate, an alkali that neutralizes the acidic chyme. Additionally, the pancreatic juices contain a large variety of enzymes that are required for the digestion of protein and carbohydrates.

The gallbladder is a small organ that aids the liver by storing bile and concentrating bile salts. When chyme containing fatty acids enters the duodenum, the bile is secreted from the gallbladder into the duodenum.

Liver

The liver is an organ within the digestive system and is responsible for maintaining sugar levels in the blood as part of homeostasis. After a large meal, the liver converts extra glucose into glycogen, a polysaccharide that stores glucose. A hormone called insulin is produced by the pancreas stimulates glycogen production. When levels of glucose in the blood drop, the liver breaks down glycogen back into glucose for the blood to circulate throughout the body. A hormone called glucagon produced by the pancreas stimulates this process. All cells of the body require glucose for cellular respiration to make energy.

The liver receives blood from the small intestines through the hepatic portal vein. After a large meal, the hepatic vein would transport glucose rich blood from the small intestines to the liver. Blood leaves the liver and returns to the heart through the hepatic vein.

4. Circulatory System:

The cardiovascular system has three major jobs in most animals

1. Transport
   • Gases (Oxygen, carbon dioxide)
   • Nutrients to cells
   • Metabolic wastes
   • Water
   • Hormones
2. Homeostasis
3. Protection
   • Blood clotting factors
   • White blood cells to fight against infection

Some invertebrates (like cnidarians) rely on a gastrovascular cavity for these functions, or diffuse gases and metabolic wastes directly through their skin. Larger and more complex animals have open or closed circulatory systems. In closed circulatory systems, the blood or equivalent transport medium is entirely within vessels in the body. Humans, other vertebrates, and squid have closed circulatory systems. In open circulatory systems, like those found in insects and many other invertebrates, blood circulates through vessels and open sinuses and can mix with interstitial fluid (this mix is called hemolymph).

Circulatory systems typically require a pump, also known as the heart, to contract and push the fluid around the body. Many animals have more than one heart for this purpose.

5. Respiratory System:

Exchange of oxygen and carbon dioxide requires a wet, thin surface for diffusion to occur. Respiratory surfaces may be internal (lungs) or external (gills) and depend on the animals environment. Small animals in wet environments can have thin skin for direct cutaneous respiration.

6. Nervous and Sensory Systems:

Nervous systems are unique to animals and are critical for detecting and interpreting information, making decisions, and regulating body functions and movements. Nervous systems are constructed from neurons and glia. Neurons are the main functional cells while glia play a variety of support roles.

Nervous systems develop as interconnected networks of cells. The largest nervous organs are the brains of vertebrates, while animals as simple as jellyfish have a ‘nerve net’. A critical concept related to nervous systems is consciousness, or ‘self-awareness’. That idea will be discussed from one perspective in the next lab, distinguishing sensation from perception.

The exercises here will review cellular function and structure, and explore several basic neural networks within the larger body. We will use a combination of models and microscopic analysis, gross anatomical dissection, and physiological exercises to study nervous systems. An overview of the components of nervous systems.

Overview of the Components of Nervous Systems:

Cellular Components
Cell Structures	Cell Functions
Neurons: Cells with membrane extensions, or neurites (axons {1 per neuron} & dendrites), interconnected at synapses. Identified by the extent of neurite branching: Multipolar = 2 or more dendrites Bipolar = 1 axon + 1 dendrite Unipolar = 1 neurite (functions as dendrite and axon, seen in specialized sensory neurons) Synapses – physical junctions between neurons, as well as between neurons and other cells, that allow for communication.	Excitable cells based on maintenance of ion—concentration gradients (for Na+ and K+ ) and membrane ion channel proteins. Membrane polarity (or membrane potential, or voltage) for a cell at rest is negative inside relative to out, based on an excess flow of K+ out of the cell. An 'action potential' is the activation of a neuron, and the membrane polarity reverses, due to the inward flow of Na+. Chemical synapses (most common type) use an action potential to signal the exocytosis of neurotransmitter chemicals (over 100 different neurotransmitters known in humans). Each neurotransmitter requires a receptor protein (multiple subtypes known for each different neurotransmitter). Electrical synapses are direct membrane junctions between cells that allow continuations of action potentials.
Glia (or glial cells, or neuroglia): Oligodendrocytes & Schwann cells Astrocytes, Satellite cells & Ependymal cells Microglia	Cells that wrap axons in myelin sheaths (glial membrane extensions) that increase action potential velocity. Cells that form borders between nervous tissues and other body tissues. Immune cells that clear cellular debris from nervous tissues.

The essential component is neurons, the major functional cells in nervous tissue. In many sensory organs, additional cells and tissues will contribute to the process of signal transduction.

Signal transduction is the process of a receptor detecting specific forms of matter or energy, and activating chemical and electrical changes in neurons. The neurons can then communicate with other neurons in the nervous system via synapses and networks to coordinate responses.

Receptor is a term used for the part of a sensory organ that detects the signal. ‘Receptor’ can refer to specific protein molecules which first interact with the matter or energy, the cell(s) that contains those proteins, or an assembly of cells in the larger organ.

Sensory Organs:

The major sensory organs can be grouped based on various characteristics, i.e. what type of matter or energy they detect and subsequently ‘transduce’ to produce our perceptions (e.g. vision, taste). Eventually, there are electrical and chemical signals within our brains. Specific organs include:

Sensory Organ (Major Receptor)	Matter/Energy Detected By Receptor	General Anatomy and Physiology	Perceived Sensation
Eye (Retina)	Visible light (Electromagnetic Radiation)	Multilayered nervous sheet within the eye with muscles and lenses for focusing	Vision
Ear (Cochlea)	Physical force (Sound)	Flexible ‘hair’ cells that release signal molecules based on waves in fluid started by the motion of the eardrum	Hearing
Ear (Semicircular Canals, Saccule, Utricle)	Physical Force	Flexible ‘hair’ cells that release signal molecules based on waves in fluid started by the motion of the head	Movement
Nose (Olfactory Epithelium)	Chemicals (‘Odorants’)	A layer of neurons at the top of the nasal cavity	Smell (’Olfaction’)
Tongue (Taste Buds)	Chemicals	Clusters of epithelial cells that release signals to neurons if specific chemicals are present (e.g. sodium ions)	Taste (‘Gustation’)
Skin (Mechanoreceptors)	Physical Force	Various neurons that respond to physical movements	Touch
Skin (Thermoreceptors)	Heat Transfer	Specific neurons that respond to increases in temperature	Hot
Skin (Thermoreceptors)	Heat Transfer	Specific neurons that respond to decreases in temperature	Cold
Muscles & Tendons	Physical Force	Neurons responding to stretch and contraction of muscles & tendons	Body Position (Proprioception)
Most of the body	Various Signals	Neurons responding to physical force, temperature, and specific chemicals to warn of (potential) damage.	Pain (‘Nociception’)

In order to investigate and understand sensory processes, we will investigate their anatomical structures (at macro- and microscopic levels) and physiological functions. An important distinction to consider is how humans can functionally separate sensation (activation of the different receptors) as compared to perception (the conscious awareness of the sensation). This distinction reveals how sensory deficits can result from damage in brain regions, even though the sensory organ is intact. Also, we may have perceptions that are only present in the brain, even though the sensory organs are silent.

7. Reproductive and Endocrine Systems:

Animal reproduction is necessary for the survival of a species. In the animal kingdom, there are innumerable ways that species reproduce. Asexual reproduction produces genetically identical organisms (clones), whereas in sexual reproduction, the genetic material of two individuals combines to produce offspring that are genetically different from their parents.

Generally, the producers of sperm (the small gamete) are called males, producers of the eggs (the large gamete) are called females. Any other characteristics that may often be associated with sex, such as chromosomes, parental care, or sexual behavior, are not universal throughout the animal kingdom. During sexual reproduction the male gamete (sperm) may be placed inside the female’s body for internal fertilization, or the sperm and eggs may be released into the environment for external fertilization.

Various internal and external structures allow animals to reproduce, including gonads, tubules to allow gametes to exit the body, and external structures for gamete deposition or transfer.

Many reproductive organs (like gonads) are also endocrine organs, and reproduction is one of the major processes the endocrine system controls. The endocrine system is the system that produces hormones, which are chemicals the body uses to communicate between organs and systems and control major processes like reproduction, growth, metabolism, and the stress response (and many more!). Many organs that are part of other systems produce hormones (like the gonads, pancreas, and brain) and there are some glands specific to the endocrine system (thyroid, pituitary, pineal). Glands are often hard to find in dissections as they tend to be small and soft and difficult to differentiate from other tissue.

8. Osmoregulatory System:

Kidneys

The kidneys are part of the urinary system. As they produce urine to release nitrogenous wastes from the body the kidneys also maintain homeostasis through pH balance and water-salt balance in osmoregulation. These bean shaped organs are located along the dorsal wall of the abdominal cavity.

Observe the kidney models available in the lab. Locate the outer renal cortex tissue and the more internal renal medulla. The renal pelvis is the area that collects the urine. Find the renal artery and the renal vein.

The functioning unit of the kidney is called the nephron. Part of the nephron is located in the cortex and part in the medulla. Use the picture below and the models in the lab to identify the following components of the nephron.

• Glomerulus
• Bowman’s capsule
• Proximal tubule
• Distal tubule
• Loop of Henle (descending limb and ascending limb)
• Collecting duct
• Peritubular capillaries

Urine production in the kidney involves four main steps:

1. Filtration: molecules move out of the glomerulus into Bowman’s capsule. Large molecules like proteins and blood cells are too big to be filtered and remain in the blood.
2. Reabsorption: glucose and amino acids move from the proximal tubule back into the blood stream through peritubular capillaries.
3. Secretion: Substances like histamines, H+, and ammonia get secreted into the nephron from the peritubular capillaries
4. Water reabsorption: both the Loop of Henle and the collecting duct reabsorb water to maintain the blood volume

Kidneys are also important in osmoregulation, maintaining an internal salt/water balance. The kidney can produce large amounts of dilute urine or small amounts of concentrated urine depending on the needs of the body. The pituitary glad produces antidiuretic hormone (ADH) which controls the concentration of urine output. ADH specifically acts on the collecting duct making it more or less permeable to water. Kidneys also play a role in pH balance.

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LICENSES AND ATTRIBUTIONS

CC LICENSED CONTENT, SHARED PREVIOUSLY

• Biology 102 Labs. Authored by: Lynette Hauser. Provided by: Tidewater Community College. Located at:[www.tcc.edu]. License: CC BY: Attribution