Anatomy & Physiology Chapter 17 - The Endocrine System

Types of Glands

1. Exocrine glands (not part of the endocrine system)

2. Endocrine glands

Exocrine glands

1. Secrets products into ducts (tubes)

2. Have a local effect

3. Eg. sweat, oil, & digestive glands

Endocrine glands

1. Ductless glands

2. Have a distant effect

3. Secrets hormones into bloodstream which affects target cells

Endorcinology

Study of the endocrine system

Endocrine system vs Nervous system

Both control and regulate the body to maintain homeostasis

Endocrine System (vs)

1. Hormones

2. Carried in bloodstream

3. Target cells with specific receptors for the hormone

4. Slow effect

5. Effect lasts longer

Nervous System (vs)

1. Neurotransmitters

2. Released at synapse during nerve implule

3. Muscles, gland, or neurons

4. Fast effect

5. Effect is shorter

Functions of the endocrine system

1. Maintains homeostasis of blood composition & volume

2. Controls reproduction

3. Regulates development, growth, & metabolism

4. Controls digestion

Hormones

Define: A chemical (produced by the endocrine system) that alters a body function

1. Carried by blood & usually affect a distant target

Control of Hormone Secretion (produce & release)

1. Hormone secretion is regulated by:

a) Hormonal stimulation

(hormone released --> gland --> different hormone released)

b) Humoral stimulation (levels of nutrients or ions in the blood)

c) Nervous stimulation

2. Negative feedback - the body secretes a hormone to reverse/fix a change in homeostasis

3. Positive feedback - the body secretes a hormone to strengthen/increase a change in homeostasis

Classes of Hormones

1. Lipid-soluble hormones (usually steroid hormones)

2. Water-soluble hormones (usually protein hormones)

Lipid-soluble hormones (usually steroid hormones)

1. Fat soluble

2. Attach to a carrier protein to be transported through blood

3. Cross cell membrane & bind to receptors inside cell

4. Eg. Sex hormones, cortisol, thyroid hormone

Water-soluble hormones (usually protein hormones)

1. Water soluble

2. Don't require a carrier protein (dissolve directly in blood)

3. Can't cross cell membrane, bind to receptors on cell surface

4. Eg. Insulin, epinephrine, pituitary hormones

Hormone interaction

1. Synergistic effect

2. Permissive effect

3. Antagonistic effect

Synergistic effect

2 hormones work together to produce a stronger effect than either hormone alone

Permissive effect

First hormone allows action of second hormone

Antagonistic effect

2 hormones have opposite effects

Eg. Insulin (lowers blood sugar) & glucagon (raises blood sugar)

The Hypothalamus

1. Major regulator of homeostasis

2. Produces releasing hormones

3. Produces inhibiting hormones

4. Also produces ADH & Oxytocin (which are released by the posterior pituitary gland)

Releasing hormones

Produced by the hypothalamus which causes anterior pituitary gland to secrete/release hormones

Inhibiting hormones

Produced by the hypothalamus which causes anterior pituitary gland to stop secreting hormones

Pituitary Gland (AKA hypophysis)

Pea-shaped structure (in the brain)

Controlled by the hypothalamus

1. Anterior lobe

2. Posterior lobe

Anterior lobe of the Pituitary Gland

Produces hormones that affect growth & reproduction

Posterior lobe of the Pituitary Gland

1. Doesn't synthesize hormones

2. Stores & releases 2 hormones for the hypothalamus

Posterior Lobe Hormones

2 following hormone produced by the hypothalamus

1. Antidiuretic hormone (ADH)

2. Oxytocin

Antidiuretic hormone (ADH) or vasopressin

1. Regulates water balance in body by causing water reabsorption in the kidneys

2. Raises blood pressure (by constricting arterioles)

3. Hyposecretion of ADH - causes diabetes insipidus

a) Symptoms: produce large amounts of urine, easily dehydrated

Oxytocin

1. Important during & after delivery of a baby

2. Effect on uterus - causes labor contractions

3. Effect on mammary glands - causes milk ejection (letdown)

4. No known roles in males

Anterior Lobe Hormones

1. Growth hormone (GH)

2. Thyroid-stimulating hormone (TSH)

3. Adrenocorticotropic hormone (ACTH)

4. Follicle-stimulating hormone (FSH)

5. Luteinizing hormone (LH)

6. Prolactin

Growth Hormone (GH) or somatotropin

1. Stimulates secretion of IGF (Insulin-like Growth Factors) which are involved in growth & repair

2. Also effects metabolism

Hyposecretion of GH in childhood causes?

Dwarfism

Hypersecretion of GH in childhood causes?

Gigiantism

Hypersecretion of GH in adulthood causes?

Acromegaly (bones abnormally thick)

Thyroid-stimulating Hormone (TSH) or thyrotropin

Stimulates secretion of thyroid gland hormones

Adrenocorticotropic Hormone (ACTH) or corticotropin

Stimulates secretion of stress hormones (glucocorticoids such as cortisol) from adrenal cortex

Follicle-stimulating hormone (FSH)

1. In females

a) Stimulates egg development

b) Stimulates estrogen production in ovaries

2. In males

a) Stimulates sperm production in testes

Luteinizing Hormone (LH)

1. In females

a) Stimulates secretion of estrogen & progesterone in ovaries

b) Triggers ovulation

2. In males

a) Stimulates testosterone production in testes

Prolactin

In females

a) Mammary gland growth

b) Breast milk production

The Thyroid Gland

1. Butterfly-shaped organ on either side of trachea

2. Secretes Thyroxine (T4) & Triiodothyronine (T3)

a) Iodine is very important in the makeup/structure of thyroid hormones

3. Secretes calcitonin

Functions of triiodothyronine & thyroxine (thyroid hormes)

1. Regulates metabolic rate

2. Help to increase body temperature

3. Regulate growth & development, especially of the nervous system

Function of Calcitonin

Decreases blood calcium level & increases Ca uptake by bones

Disorders of the Thyroid Gland

1. Hyperthyroidism

2. Hypothyroidism

3. Goiter

Hyperthyroidism

Overactive thyroid gland

1. Caused by: *excess TSH* or *Graves disease*

2. More common in women

Graves Disease

An autoimmune disorder in which thyroid gland over produces hormones

Hypothyroidism

Underactive thyroid gland

1. Congenital hypothyroidism

2. Myxedema

Congenital hypothyroidism

Caused by thyroid hormone deficiency during fetal development/infancy

1. Results in severe intellectual disability

2. Results in dwafism

Myxedema

Thyroid hormone deficiency during adulthood

1. More common in women

Goiter

Enlarged thyroid gland

1. Caused by: Thyroid disorder or low amount of iodine in diet

Parathyroid Glands

4 small round glands found on back of thyroid gland

1. Secrete Parathyroid Hormone

2. Increases blood calcium levels

Adrenal Glands

1. Pair of pyramid-shaped glands

2. One on top of each kidney

Regions inside the adrenal glands

1. Adrenal cortex - outer edge

2. Adrenal medulla - inner region

Hormones secreted by the adrenal medulla

1. Secretes Epinephrine (adrenaline) & Norepinephrine

2. Sympathetic nervous system stimulates their release

3. Epinephrine and norepinephrine are responsibe for effects of fight or flight response

Hormones secreted by the adrenal cortex

1. Aldosterone (mineralocortocoids)

2. Cortisol (glucocorticoids)

3. Androgens (gonadocorticoids)

Aldosterone (mineralocorticoids)

Increase reabsorption of Na+ and water in kidneys (prevents dehydration and increase blood pressure)

Cortisol (glucocorticoids)

1. Regulates metabolism

2. Provides resistance to stress

3. Has an anti-inflammatory effect

4. High amounts of cortisol also depress the immune system

Androgens (gonadocorticoids)

1. Growth of hair at puberty

2. Contributes to sex drive in females

The Pancreas

1. both an endocrine & exocrine gland

2. Located behind the stomach

Pancreatic islets

1. Alpha cells secrete *Glucagon*

a) Glucagon *raises* blood glucose level by causing the liver to release stored glucose

2. Beta cells secrete *Insulin*

a) Insulin *lowers* blood glucose by causing cells to take in glucose

b) Insulin promotes anabolism

Diabetes Mellitus

Define: Metabolic condition marked by inadequate uptake of glucose from blood

1. Symptoms

a) Polyuria

b) Glucosuria

c) Polydipsia

d) Polyphagia

e) hyperglyciema

Polyuria

Excessive urine production

Glucosuria

Glucose in the urine

Polydipsia

Excessive thirst

Polyphagia

Excessive eating

Hyperglycemia

Elevated blood glucose

Type 1 Diabetes Mellitus

Insulin dependent

1. Autoimmune disorder in which beta cells are destroyed. As a result, pancreas can't produce insulin.

2. Diagnosed in people younger than 20

3. When insulin deficient, the body acts like it's starving which causes ketoacidosis

4. Ketoacidosis makes blood pH turn acidic which can cause death

5. Other complications - cardiovascular problems, blindness

6. Treatment - Insulin injections

Type 2 Diabetes Mellitus

Non-insulin dependent

1. Body is less sensitive to insulin (doesn't properly use it)

2. Usually diagnosed in overweight people over 35

3. Treatment - diet, exercise, weight loss, oral medications

Gestational Diabetes

1. Diabetes caused by hormone changes during pregnancy

2. Goes away after delivery

3. Leads to large birth weight of child

Gonads (Ovaries and Testes)

1. Ovaries (in females)

a) Secrete estrogens (Eg. estradiol) & progesterone

b) Responsible seconddary sex characteristics, regulates menstrual cycle, maintain pregnancy, involved in lactation

2. Testes (in males)

a) Secrete testosterone

b) Responsible for secondary sex characteristics & sperm production

Pineal Gland

1. Part of epithalamus (in brain)

2. Secrets *Melatonin* - helps control the body's biological clock (sleep-wake cycles)

3. Overproduction of melatonin - causes seasonal affective disorder (seasonal depression caused by short days of winter; treatment is light therapy)

Prostaglandins

1. Produced by all cells except RBCs

2. Have many effects in the body, including smooth muscle contraction, inflammation, fever, & pain

Leukotrienes

1. Produced by all cells except RBCs

2. Involved in inflammation, especially of the airway

Growth Factors

1. Stimulate cell growth & division

2. If mutated, can cause cancer