chapter 9 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 isthmus

c.    Produces two hormones

                                                  i.    Thyroid hormone (TH)

1.     Major metabolic hormone (rate at which glucose is burned in the cells)…composed of two active iodine containing hormones:

a.    Thyroxine (T₄)-secreted by thyroid follicles

b.    Triiodothyronine (T₃)-hormone that controls growth, development, metabolism, body temp., heart rate

                                                ii.    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 remover 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: sit 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 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

a.    Produced in the middle layer of the adrenal cortex

b.    Promote normal cell metabolism

c.    Help resist long-term stressors

d.    Released in response to increased blood levels of ACTH

3.    Sex hormones- secreting area

a.    Produced in the inner layer of adrenal cortex

b.    Small amounts are made throughout life

c.    Mostly androgens(male sex hormones) but some estrogens(female sex hormones) are also formed

4.    Disorders

a.    Addison’s disease results froms hyposecretion of all adnrenal cortex hormones

b.    Hyperaldosteronism may result from an ACTH-releasing tumor

c.    Cushing’s syndrome –results from a tumor in the middle cortical area of the adrenal cortex

d.    Masculinization results from hypersecretion of sex hormones

                                                ii.    Adrenal medulla –inner neutral tissue region

1.     Produce two similar hormones (catecholamines)

a.    Epinephrine (adrenaline)

b.    Norepinephrine (noradrenaline)

c.    Fight or flight-these hormones prepare the body to deal with short-term stress

d.    Increasing heart rate, blood pressure, glucose levels

e.    Dilating small passageways of lungs

4.    Pancreatic islets (islands of endocrine cells; pancreas is also exocrine)-The pancreas is a mixed gland and has both endocrine and exocrine functions

a.    Insulin- allows glucose to cross plasma membranes into cells from beta cells

b.    Glucagon-allows glucose to enter the blood from alpha cells

c.    These hormones are anatagonists that maintain blood sugar homeostasis

d.    Disorders:  diabetes

                                                  i.    Type 1 – juvenial diabetes.

                                                ii.    Type 2 – pancreas as put in overdrive, can be reversed by diet and exercise or insulin.

5.    Pineal gland

a.    Location – found on 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 hormone:

1.     Estrogen

a.    Stimulate the development of secondary female characteristics

b.    Mature female reproductive organs

c.    Along with progesterone, estrogen 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

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