Endocrine System Chapter 30 AP Biology 2012

Endocrine System Consists of cells that produce and release chemical signals called hormones.

In the body Endocrine vs. Exocrine Out of the body Endocrine Signals Exocrine Signals Secrete substances into the extracellular fluid Done by endocrine cells or secretory organs called endocrine glands (testes, thyroid) Example; Signaling molecules Secrete substances into a duct or internal body cavity that communicates with the external world Example: saliva, sweat In the body Out of the body

Hormones “long distance” endocrine signals that are released into the bloodstream and circulate through the entire body 3 chemical groups Peptide and protein hormones Steroid hormones Amine hormones

Peptide and protein hormones Large Water soluble – therefore easily transported in the blood Packaged in vesicles and released by exocytosis Most hormones are this type Examples: insulin and growth hormone

Steroid Hormones Made from cholesterol (look similar too!) Lipid soluble Do not dissolve well in blood plasma so they are bound to carrier proteins for transport in the blood Found inside target cells Example: aldosteroids, cortisol, testosterone

Amine hormones Small molecules Made from single amino acids Could be polar or nonpolar depending on the R group of the amino acid it was synthesized from Example: Tyrosine  epinephrine and thyroxine

30.2 Review That same hormone could cause very different responses in different types of cells

Fight or Flight Response Rapid physiological response to sudden danger or highly stressful situations Involves epinephrine (adrenaline) and norepinephrine (noradrenaline)

What’s really happening Epinephrine and norepinephrine bind to a set of adrenergic receptors (G proteins!) 2 categories Alpha Beta Have different affinities for ephinephrine and norepinephrine!

Adrenergic Receptors Alpha Beta It causes blood vessels in the skin to constrict, causing cold hands and feet Shut off the secretion of digestive enzymes and decrease blood flow through the gut (digesting lunch waits) In heart cells, it causes a faster and stronger heartbeat (thus pumping more blood) Cause arterioles in skeletal muscles to enlarge so increased blood flow goes there enabling you to run Breakdown of glycogen in liver for quick energy! Breakdown of fats to yield fatty acids – another source of energy!!

Hormone receptors are regulated Downregulation – makes the cells less sensitive to the hormone, causing cells to ignore the excess hormone Example in diabetes High levels of insulin downregulates the production of insulin receptors in body

Hormone receptors are regulated upregulation – occurs if hormone secretion is chronically low; cell makes more receptor for that hormone Example in high blood pressure People who are regular medication (beta blockers) Let’s say they go off the medication suddenly, the effects of the receptors are amplified, resulting in heightened anxiety and blood pressure Explains why dosages for medications are carefully supervised. 

30.3 Nervous system and Endocrine System are linked. This is done by the Pituitary Gland!

Pituitary Gland Endocrine gland Attached to a region of the brain called the hypothalamus Has 2 parts Anterior Pituitary Posterior Pituitary

Anterior Pituitary Releases 4 tropic hormones Hormones that direct and control the activities of other endocrine glands TSH – thyroid stimulating hormone LH – luteinizing hormone FSH – follicle stimulating hormone ACTH – adrenocorticotropic hormone Produces peptide hormones Prolactin (stimulates milk production) Growth hormone (promotes growth) Overproduction causes GIGANTISM Underproduction causes pituitary dwarfish

Posterior Pituitary Releases 2 neurohormones ADH Oxytocin Increases amount of water conserved by the kidneys When high, kidneys produce little volume of highly concentrated urine When low, kidneys produce large volume of dilute urine Oxytocin Stimulates uterine contractions during birth Stimulates flow of milk from mother’s breasts Promotes pair bonding and trust; “cuddle hormone”

Negative Feedback Loop Corticotropin-releasing hormone (CRH) from hypothalamus stimulates release of adrenocorticotropic hormone (ACTH) from anterior pituitary, which in turn stimulates release of hormone cortisol from adrenal glands. Once cortisol is released, it circulates thru body, where it directly inhibits further release of both CRH and ACTH This maintains a constant level of cortisol

30.4 Mammal hormones

Thyroid Glands Wrap around trachea (windpipe) Produce two hormones Thyroxine Calcitonin

Thyroxine Amine hormone made from amino acid tyrosine Known as T4 – for 4 iodine atoms (T3 is a nearly identical hormone) Raises metabolic rate Lipid soluble Critical during growth and development Insufficient amount during growth results in physical and mental retardation - cretinism

Thyroxine continued… Levels are controlled by hypothalamus and anterior pituitary Hypothalamus releases thyrotropin-releasing hormone (TRH) which stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH) which stimulates thyroid gland to produce and release thyroxine Regulated by a negative feedback loop (like cortisol)

Goiters Is an enlarged thyroid gland associated with Hyperthyroidism (too much thyroxine) Hypothyroidism (too little thyroxine)

Hyperthyroidism Caused by an antibody binding to and activating TSH receptors, causing uncontrolled production and release of thyroxine Symptoms: High metabolic rate Nervous and jumpy Hot Eyes bulge due to buildup of fat behind eye

Hypothyroidism Caused by a lack of circulating thyroxine to turn off TSH production Caused by lack of iodine in diet Symptoms: Low metabolism Intolerance of cold Sluggish Greatly reduced by widespread use of iodized table salt

Homeostasis of Calcium is VITAL!! Why? trigger neurotransmitter release Muscle contraction

Calcium levels Too little Ca Too much Ca Muscle spasms Seizures Nervous system to be depressed Muscles and heart to weaken or stop 99% of Calcium is in bone 1% in cells – so this tiny pool of Ca must be maintained!!

3 Mechanisms the body does to maintain Ca levels Deposition or resorption of bone Excretion or retention of calcium by kidneys Absorption of Calcium from digestive tract These mechanisms Are controlled By calcitonin, calcitriol And parathyroid hormone (PTH)

Calcitonin Released by thyroid gland Lowers the concentration of Ca in the blood by regulating bone turnover Bone is continuously being made (resorption of old bone and synthesizing new bone) Osteoclasts break down bone and release Ca into blood Osteoblasts take up Ca and put it in new bone Decreases activity of osteoclasts Does not play major role in adults, but does in younger actively growing individuals

Calcitriol Made from Vitamin D in the liver and kidneys Vitamin D is obtained from the sun (UV waves in sunlight convert cholesterol into vitamin D) Otherwise Vitamin D must be obtained from diet Hormone that stimulates the cells of the digestive tract to absorb calcium from ingested food

Parathyroid Hormone Most important for homeostasis Glands located to the rear of the thyroid Synthesis is triggered when blood calcium fall below set point Increases concentration of calcium 3 ways Stimulates bone turnover activities of osteoclasts and osteoblasts Stimulates kidney to reabsorb Calcium Increases body absorption of calcium from food by activitating the synthesis of calcitriol from vitamin D

Adrenal Glands Sit above the kidneys 2 of them Has a core, called the adrenal medulla, which produces epinephrine and norepinephrine This release is under control of the nervous system Both hormones increase heart rate and bp Cause fat and liver cells to release metabolic fuel

Arenal Cortex Surrounds the adrenal medulla Produces 2 corticosteroid hormones Mineralocorticoids Glucocorticoids Mineralocorticoids Increase salt and water balance of the extracellular fluid Example: aldosterone – stimulates the kidneys to conserve sodium and excrete potassium Glucocorticoids Increase blood glucose concentrations and affect macromolecule metabolism Example: cortisol – critical for mediating long term metabolic responses to stress

Gonads Male – testes; Female – Ovaries Both produce hormones as well as the gametes (sperm and egg) Male hormones produced are called androgens, Example: testosterone Female hormones produced are estrogen and progesterone ** Both sexes produce both testosterone and estrogen

Sexual Differentiation Y chromosome – embryonic glands begin producing testosterone in 7th week of development and a peptide hormone called MIS (Mullerian-inhibiting substance) Testosterone causes testes and ducts develop and MIS induces apoptosis of cells of female reproductive ducts, so they disappear So androgens are required for male development in humans

Puberty Time of sexual maturation and dramatic physical transformation around age 12-13 Controlled by gonadotropins Contain two hormones, LH (luteinizing hormone) and FSH (follicle-stimulating hormone) Under control of a hypothalamic neurohormone called gonadotropin-releasing hormone GnRH Before puberty, the hypothalamus is producing very low levels of GnRH

Puberty Continued… Initiated by a reduction in the sensitivity of GnRH producing cells by negative feedback The reduced sensitivity overcomes the negative feedback and so GnRH release increases, stimulating production of gonadotropins and hence production of sex steroid hormones

Puberty Continued… In females, increased levels of LH stimulates the ovaries to increase estrogen production This initiates development of enlarged breasts, vagina and uterus, broadened hips, increased fat, pubic hair, and menstrual cycle In males, increased levels of LH stimulates the testes to produce testosterone This initiates the voice to deepen, facial and body hair, muscle mass increase, testes and penis grow larger