Lab 12: Endocrine System

Introduction:

An animal’s endocrine system controls body processes through the production, secretion, and regulation of hormones, which serve as chemical “messengers” functioning in cellular and organ activity and, ultimately, maintaining the body’s homeostasis. The endocrine system plays a role in growth, metabolism, and sexual development. In humans, common endocrine system diseases include thyroid disease and diabetes mellitus. In organisms that undergo metamorphosis, the process is controlled by the endocrine system. The transformation from tadpole to frog, for example, is complex and nuanced to adapt to specific environments and ecological circumstances.

Table 1: Different Classes of Hormones
Hormone Class	Components	Example(s)
Amine Hormone	Amino acids with modified groups (norepinephrine's carboxyl group is replaced with a benzene ring.)
Peptide Hormone	Short chains of linked amino acids.
Protein Hormone	Long chains of linked amino acids.
Steroid Hormone	Derived from the lipid cholesterol

Maintaining homeostasis within the body requires the coordination of many different systems and organs. Communication between neighboring cells, and between cells and tissues in distant parts of the body, occurs through the release of chemicals called hormones. Hormones are released into body fluids (usually blood) that carry these chemicals to their target cells. At the target cells, which are cells that have a receptor for a signal or ligand from a signal cell, the hormones elicit a response. The cells, tissues, and organs that secrete hormones make up the endocrine system. Examples of glands of the endocrine system include the adrenal glands, which produce hormones such as epinephrine and norepinephrine that regulate responses to stress, and the thyroid gland, which produces thyroid hormones that regulate metabolic rates. Although there are many different hormones in the human body, they can be divided into three classes based on their chemical structure: lipid-derived, amino acid-derived, and peptide (peptide and proteins) hormones.

If endocrine glands are not functioning properly the body can be out of homeostasis and a patient may be diagnosed with an endocrine system disease or disorder (Figure 1). In today’s lab, you will be using your knowledge of the endocrine system and various hormones to diagnose patients. The objectives of today’s lab are to identify the main human endocrine glands, diagnose “patients” with endocrine diseases based on their symptoms, and write a case study for another endocrine disease.

Exercise 1:

Endocrine glands function by releasing hormones that move through the blood to targets throughout the body. The structures labeled A-J in Figure 2 are true endocrine glands; however, other tissues and organs, like adipose tissue and your kidneys and heart, can also produce hormones. Identify the endocrine glands in the figure and then match them with the hormone(s) they produce.

_____ Adrenocorticotropic hormone (ACTH) _____ Insulin

_____ Antidiuretic hormone (ADH) _____ Luteinizing hormone (LH)

_____ Aldosterone _____ Melatonin

_____ Cortisol _____ Oxytocin

_____ Epinephrine _____ Progesterone

_____ Estrogen _____ Prolactin

_____ Follicle stimulating hormone (FSH) _____ Testosterone

_____ Glucagon _____ Thyroxine

_____ Growth hormone (GH) _____ Thyroid stimulating hormone (TSH)

Exercise 2:

Endocrine disorders can often be difficult to diagnose because many can present very similar symptoms. Diagnosis often requires a combination of lab work and a patient’s history. On Table 2, you will see several different endocrine disorders with common physical symptoms and lab results. Use this information to answer the questions below.

Table 2: Endocrine Disorders
Disorders	Symptoms	Lab Test Results
Acromegaly	Enlarged hands and feet, excessive sweating, fatigue, muscle weakness, pain, limited joint mobility	Elevated levels of insulin, like growth factor I
Addison's Disease	Fatigue, increased pigment in the skin, weight loss, muscle weakness	Low sodium, high potassium, high ACTH, low cortisol in the blood
Cushing's Syndrome	Backache, anxiety, muscle weakness, extra fat deposits on the back of the neck and upper back (aka "buffalo hump"), females may experience irregular menstrual cycle	High levels of cortisol in the blood
Diabetes Insipidus	Frequent urination, excessive thirst	Normal blood glucose level, no glucose in the urine, low ADH level in the blood
Hyperparathyroidism	Excessive thirst, weak or broken bones, fatigue, nausea	High calcium and parathyroid hormone levels in the blood
Hyperthyroidism	Elevated body temp, extreme sweating, nervousness, rapid heart rate, weight loss, irregular menstrual cycle in females	High thyroxine and low TSH in the blood
Hypothyroidism	Fatigue, muscle weakness, depression, weight gain, low body temperature, intolerant of cold	Low thyroxine and high TSH in the blood
Polycystic Ovarian Syndrome (PCOS)	Acne, unwanted hair growth, weight gain, fatigue, infertility, mood changes, sleep problems	Elevated levels of testosterone and LH, low levels of FSH in blood
Type I Diabetes Mellitus	Frequent urination, excessive thirst, weight loss	Glucose in urine, elevated blood glucose, islet cell antibody in the blood
Type 2 Diabetes Mellitus	Frequent urination, excessive thirst	Glucose in urine, elevated blood glucose, no islet cell antibody in the blood

Question:

1. What is the most frequent physical symptom of the disorders described above?

2. Why are blood tests used to diagnose endocrine disorders?

3. Why is it so important to consider age and sex when diagnosing an endocrine disorder?

Case Study 1:

A 37-year-old woman goes to her doctor and complains of anxiety, muscle weakness, and depression. Which of the disorders listed on the table above could explain her symptoms? What other symptoms might you look for or what other tests might you run to distinguish between these disorders?

Case Study 2:

A 34-year-old man complains he is tired a lot and he has lost a substantial amount of weight over the past few months. A routine blood test shows low sodium levels, but his blood glucose levels are normal. What test would you order next? Why? What results could help you make a diagnosis?

Case Study 3:

Your patient is a 28-year-old woman who has complained of menstrual irregularities and infertility despite actively trying to get pregnant for 14 months. She also mentioned that she has to wax her face a lot due to hair growth. How would you diagnose this patient? Which lab result may explain the hair growth? What does this patient have to be careful of developing in the future?

Case Study 4:

A seemingly healthy 42-year-old-man comes into the ED with a broken arm. The doctor set the bone with no issue but is concerned that the patient’s bones are unusually weak. The man follows up with an endocrinologist and during that appointment, he reports fatigue and nausea. What disorder could this patient have? How could you confirm the diagnosis?

Table 1 from WikiCommons, Figure 1 from WikiCommons, and additional information from OpenStax Biology. This lab is licensed under a Creative Commons Attribution License License (3.0)