Chapter 10 Study Guide

The Endocrine System

By: Sarah Genet

Endocrine System

• Controls body functions via hormones.

So let’s say there’s too much glucose in your blood. Your pancreatic islets cells send insulin into the blood which tells your cells to start absorbing all the glucose, thereby decreasing the concentration of glucose in your blood. The hormone in this situation is insulin, and you can deduce how it is affecting bodily functions.

Pretty big deal, no? If a patient’s pancreatic islet cells stop making insulin, or if they can no longer act on their target cells, that patient has diabetes mellitus. Do you know someone with diabetes?

Two types of Glands

• The endocrine system secretes hormones using endocrine glands (kind of makes sense, no?) These are glands which lack ducts. Ducts are like tubes which carry hormones into the blood so they can be circulated around the body and distributed.

• So what is the other possible type of gland?

Not endocrine, but exocrine.

Hormone Types

1. Nonsteroid Hormones – Proteins, short chain amino acids or single amino acids

1. Proteins are water soluble and therefore cannot pass through the cell membrane. Therefore nonsteroid hormones affect the activity of the cell via a secondary messenger system (see: lock and key model and cyclic AMP)

2. Steroid Hormone – Lipid soluble steroid hormone

1. Can pass through a cell’s cell membrane, travel through the cytoplasm, enter the nucleus and act on DNA (see: hormone receptor complex)

Prostaglandins

• Not actually hormones….hormones are produced in one location (for example, insulin is made only in the pancreas) but prostaglandins are produced in many places, throughout the body

• Prostaglandins are frequently produced in tissues and act locally. In other words, they are produced in a tissue and diffuse a short distance to act on cells within that tissue

Regulation of Hormone Secretion

• Negative feedback: the output of a system acts to oppose changes to the input of the system– Ex) During periods of high blood sugar pancreatic

islet cells secrete insulin in order to decrease blood sugar levels and bring them back to normal.

• Positive feedback: amplify changes to the system– Ex) Oxytocin increases the force of contractions

during labor

Endocrine Glands

• Hypothalamus• Pituitary• Pineal• Thyroid• Parathyroid• Thymus• Adrenal• Pancreas• Ovaries (female), Testes (male)

Pituitary Gland

• Located in sella turcica of the Sphenoid bone• Two parts

– Anterior pituitary,aka adenohypophysis– Posterior pituitary, aka neurohypophysis

Pituitary Hormones

Anterior Pituitary

FLAT (all tropic hormones)

1. FSH

2. LH

3. ACTH

4. TSH

PG

5. Prolactin

6. GH

Posterior Pituitary

1. ADH

2. Oxytocin

Pituitary Disorders

• Hyperglycemia: too much sugar in blood. One cause is too much GH

• Diabetes Insipidus: dehydration and electrolyte imbalance due to hyposecretion of ADH

Hypothalamus

• Nervous and endocrine function

• Nervous – Specialized neurons produce ADH and oxytocin (to posterior pit.)

• Endocrine - Releases releasing and inhibiting hormones. These travel to the anterior pituitary and cause the ant. Pit. to release or inhibit the production/release of hormones.

Thyroid Gland

• Located in neck below the larynx• Secretes T3 (triiodothyronine) and T4

(thyroxine). T3 has 3 molecules of iodine and T4 has 4 molecules of iodine. – Stores T3 and T4 in the follicle. Most endocrine

organs do not store hormones, so this function is unique!

• Secretes calcitonin – decreases concentration of calcium in the body. This hormone is used to prevent an excess of calcium in the blood, a condition known as hypercalcemia.

Example of negative feedback

• In this diagram T3 and T4 perform negative feedback on the anterior pituitary and the hypothalamus, causing them to decrease their release of TSH and TRH.

Thyroid Hormone Abnormalities

• Hyperthyroidism – over secretion of thyroid hormone

• Hypothyroidism – under secretion of thyroid hormone– Simple Goiter – enlargement of thyroid gland

caused by low dietary intake of iodine– Cretinism – hyposecretion of thyroid hormone

during formative years– Myxedema – hyposecretion of thyroid

hormone later in life.

Parathyroid Gland

• Located on the back of the thyroid

• Secretes parathyroid hormone (PTH) – increases blood calcium levels.

• What hormone decreases blood calcium levels?

Adrenal Gland

• Composed of two endocrine glands: the adrenal cortex and the adrenal medulla

Adrenal Gland

• Adrenal Cortex - secretes corticoids:– mineralocorticoids

(MC). ex) aldosterone– Glucocorticoids (GC)

ex) cortisol aka hydrocortisone

– Sex hormones ex)androgens

• Adrenal Medulla– Epinephrine and

norepinephrine

Adrenal Medulla Abnormalities

• Cushing’s Syndrome – overproduction of adrenal cortex hormones. Symptoms include moon-face, buffalo hump on upper back, elevated blood sugar and frequent infections (Seen in photo below)

• Addison’s Disease – hyposecretion of adrenal cortex hormones. Results in muscle weakness, reduced blood sugar, nausea, loss of appetite and weight loss

Pancreatic Islet

• Located in exocrine pancreas.

• Two types – alpha and beta cells. Alpha release glucagon and beta release insulin.– Glucagon increased blood glucose

concentration via liver glycogenolysis– Insulin decreased blood glucose

concentration

• Secrete pancreatic enzyme juice.

Diabetes Mellitus

• Type I diabetes – increase in blood glucose levels due to hyposecretion of insulin

• Type II diabetes – increase in blood glucose due to an abnormality of insulin receptors. Sometimes accompanied by hyposecretion of insulin.

• Diabetes Mellitus results in glycosuria - glucose in the urine. Doctors can diagnose diabetes by checking the blood or urine.

Sex Glands - Female• Female Sex Glands – two ovaries

– Composed of two parts: 1. the follicle – secretes estrogen and the egg or

ova developes here1. Estrogen – involved in development and maturation of

breast and external genitalia, development of adult female contours (hips, curves) and initiation of the menstrual cycle

2. Corpus Luteum – secretes

progesterone and some estrogen.

Sex Glands - Male• The testes are made of many cell types. One

cell type, the interstitial cell, makes testosterone which is the male sex hormone.

• Testosterone – “masculinizing hormone” – maturation of external genitalia, beard growth, changes in voice at puberty, muscular development and male contour.

Thymus• Located in the mediastinum (adults) or may

extend up into the neck as far as the bottom of the thyroid gland (infants)

• Composed of a cortex and medulla. What other organ contains a cortex and medulla?

• Both parts are composed of lymphocytes; the thymus plays a critical role in defense against infections

• Produces thymosin

Placenta

• Temporary endocrine structure present during pregnancy• Produces chorionic gonadotropins (tropic hormones produce by the chorion),

estrogen and progesterone• During the earlier weeks of pregnancy the

placenta excretes large amounts of chorionic gonadotropins into the blood. So, when a woman takes a pregnancy test, it is looking for the presence of this hormone because some of the hormone is secreted in the urine

Pineal Gland• Located near the roof of the third ventricle in the brain.• Easily located in a child but not in an adult. This is

because the gland becomes encrusted with calcium deposits as a person ages.

• Makes many hormones, the most important one being melatonin.

• Melatonin – inhibits the tropic hormones which affect the ovaries and is throught to be involved in regulating the onset of puberty and the menstruation in women. The release of melatonin is increased during the night and decreased during the day.

Additional Endocrine Structures

• Atrial Natriuretic Hormone – secreted by cells in the hearts’ atria (upper chambers of the heart). Regulates fluid and electrolytes in the body and is an antagonist to aldoesterone. (Aldosterone causes the body to hold on to sodium and water while ANH stimulates the loss of sodium and water.

• Leptin – secreted by fat storing cells. Regulates how hungry/full we feel and how fat is metabolized by the body.