Chapter 9, The Endocrine System, Part B

Anatomy & Physiology – Chapter 9 Part B
Endocrine System
1. Thyroid gland
a. Found at the base of the throat
b. Consists of two lobes and a connecting tissue
c. Produces two hormones
i. Thyroid hormone (TH)
1. Major metabolic hormone (rate at which glucose is burned in the cells)
ii. Composed of two active iodine-containing hormones:
1. Thyroxine (T4 )—secreted by thyroid follicles
2. Triiodothyronine(T3)
iii. Thyroid hormone disorders:
1. Goiters:
a. Thyroid gland enlarges due to lack of iodine
b. Salt is iodized to prevent goiters
c. Most common in poor, third world countries
2. Cretinism:
a. Caused by hyposecretion of thyroxine
3. Myxedemi:
a. Caused by hypothyroidism in adults
b. Results in physical and mental slugishness
4. Graves’ disease:
a. Caused by hyperthyroidism
iv. Calcitonin
1. Decreases blood calcium levels by causing its deposition on bone
2. Antagonistic to parathyroid hormone
2. Parathyroid gland
a. What and where: tiny masses on the posterior of the thyroid
b. Secretes parathyroid hormone (PTH) which:
i. Stimulates osteoclasts to remove calcium from bone
ii. Stimulates the kidneys and intestine to absorb more calcium
iii. Raises calcium levels in the blood
iv. See Figure 9.10
3. Adrenal glands
a. Location: sits on top of the kidneys
b. Each has two anatomical & physiological regions:
i. Adrenal cortex: outer glandular region has three layers:
1. Mineralocorticoids (aldosterone) secreting area
a. Produced in the outer adrenal cortex
b. Regulate mineral content in blood
c. Regulate water and electrolyte balance
d. Target organ is the kidney
e. Stimulated by rennin and aldosterone
f. Inhibited by atrial natriuretic peptide (ANP)
2. Glucocorticoids secreting area (including cortisone and cortisol)
a. Produced in the middle layer of the adrenal cortex
b. Promote normal cell metabolism
c. Help resist long-term stressors
d. Released in the response to increase blod levels of ACTH
3. Sex hormones secreting area
a. Produced in the inner layer of the adrenal cortex
b. Small amounts are made throughout life
c. Mostly androgens (male sex hormones) are made but some estrogens (female sex hormones) are also formed
4. Disorders
a. Addison’s disease
i. Results from hyposecretion of all adrenal cortex hormones
ii. Bronze skin tone, muscles are weak, burnout, susceptibility to infection
b. Hyperaldosteronism
i. May result from an ACTH-releasing tumor
ii. Excess water and sodium are retained leading to high blood pressure and edema
c. Cushing’s syndrome
i. Results from a tumor in the middle cortical area of the adrenal cortex
ii. “Moon face,” “buffalo hump” on the upper back, high blood pressure hyperglycemia, weakening of bones, depression
d. Masculinization
i. Results from hypersecretion of sex hormones
ii. Beard and male distribution of hair growth
ii. Adrenal medulla
1. Produce two similar hormones (catecholamines)
a. Epinephrine (adrenaline)
b. Norepinephrine (noradrenaline)
c. Fight or flight
d. These hormones prepare the body to deal with short-term stress (“fight or flight”) by increasing heart rate, blood pressure, blood glucose levels
e. Dilating small passageways of lungs
4. Pancreatic islets
a. The pancreas is a mixed gland and has both endocrine and exocrine functions
b. The pancreatic islets produce hormones:
i. Insulin—allows glucose to cross plasma membranes into cells form beta cells
1. Lowers blood sugar
ii. Glucagon—allows glucose to enter the blood from alpha cells
1. Raises blood sugar
iii. These hormones are antagonists that maintain blood sugar homeostasis
c. Disorders: diabetes
i. Type 1 – juvenile diabetes (diagnosed at a very young age), usually born with it. Pancreas cannot and will not ever produce insulin.
ii. Type 2 – pancreas has been put in “over drive”, pancreas just cannot produce enough insulin. Can be monitored and possibly rid of by watching your weight and what you eat.
5. Pineal gland
a. Location
i. Found on the third ventricle of the brain
b. Secretes melatonin:
i. Helps establish the body’s wake and sleep cycles
ii. Believed to coordinate the hormones of sexual maturation and fertility in humans
6. Thymus gland
a. Located posterior to the sternum
b. Largest in infants and children
c. Produces thymosin:
i. Matures some types of white blood cells
ii. Important in developing the immune system
7. Gonads
a. Ovaries
i. Produce eggs
ii. Produce two groups of steroid hormones:
1. Estrogens
a. Stimulate the development of secondary female characteristics
b. Mature female reproductive organs
c. Along with progesterone, estrogens also:
i. Promote breast development
ii. Regulate menstrual cycle
2. Progesterone:
a. Acts with estrogen to bring about the menstrual cycle
b. Helps in the implantation of an embryo in the uterus
c. Helps prepare breasts for lactation
b. Testes
i. Produce sperm
ii. Produce androgens, such as testosterone (most important androgen)
1. Responsible for adult male secondary sex characteristics
2. Promotes growth and maturation of male reproductive system
3. Required for sperm cell production
8. Other hormone-producing organs/tissues
9. Placenta – nurturing structure for developing fetus; attached to umbilical cord
a. Produces
b. Some hormones
c. Produces human chorionic gonadotropin (hCG)
10. Developmental aspects of the endocrine system
a. Most organs
b. Menopause
c. Problems
d. Growth hormone
e. Endocrine glands