Endocrine System Chapter 32

Homeostasis Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level Regulation of room temperature by a thermostat is analogous to homeostasis

Sensor/ control center: Thermostat turns heater off. Response: Heating stops. Room temperature decreases. Stimulus: Room temperature increases. Set point: Room temperature at 20C Figure 32.4 A nonliving example of temperature regulation: control of room temperature Stimulus: Room temperature decreases. Room temperature increases. Response: Heating starts. Sensor/ control center: Thermostat turns heater on. 3

Sensor/control center: Thermostat in hypothalamus Response: Sweat Blood vessels in skin dilate. Stimulus: Increased body temperature Body temperature decreases. Homeostasis: Internal body temperature of approximately 36–38C Body temperature increases. Stimulus: Decreased body temperature Figure 32.8 The thermostatic function of the hypothalamus in human thermoregulation Response: Blood vessels in skin constrict. Sensor/control center: Thermostat in hypothalamus Response: Shivering 4

Homeostasis Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulus Homeostasis moderates, but does not eliminate, changes in the internal environment Set points and normal ranges for homeostasis are usually stable, but certain regulated changes in the internal environment are essential

Animation: Negative Feedback Right click slide / Select play

Animation: Positive Feedback Right click slide / Select play

Feedback Mechanisms negative feedback helps to maintain homeostasis positive feedback enhances an already existing response

Nervous vs Endocrine Nervous immediate acts thru electrical impulses and neurotransmitters effect is localized and short duration Endocrine acts thru chemicals – hormones act on cells with receptors effect is generalized and long term duration

Endocrine cell Cell body of neuron (a) Signaling by hormones (b) Signaling by neurons Stimulus Stimulus Endocrine cell Cell body of neuron Nerve impulse Axon Hormone Signal travels everywhere. Signal travels to a specific location. Blood vessel Nerve impulse Figure 32.9 Signaling in the endocrine and nervous systems Axons Response Response 10

Neuroendocrine Pathways Hormone pathways that respond to stimuli from the external environment rely on a sensor in the nervous system In vertebrates, the hypothalamus integrates endocrine and nervous systems Signals from the hypothalamus travel to a gland located at its base, called the pituitary gland Anterior pituitary Posterior pituitary 11

Hypothalamus region in the forebrain regulates internal environment contains hormone-secreting cells produces and releases ADH, Oxytocin interacts with pituitary contains releasing hormones pituitary gland

Pituitary Gland pea-sized gland at base of hypothalamus contains stimulating hormones two lobes posterior lobe stores and secretes hormones synthesized in the hypothalamus antidiuretic hormone (ADH) released in response to blood being concentrated goes to kidney * causes water to be reabsorbed negative feedback

Pituitary Gland Oxytocin uterine contractions milk letdown positive feedback

Posterior pituitary function Pituitary Gland Posterior pituitary function

Pituitary Gland anterior pituitary affecting other glands thyroid stimulating hormone (TSH) Triiodothyronine / tyroxine * both regulate metabolism and growth rate increases

Pituitary Gland adrenocorticotropic hormone (ACTH) adrenal cortex release of cortisol raises blood sugar levels counteracts inflammation gonadotropic hormone follicle stimulating (FSH) luteinizing hormone (LH) stimulates ovaries and testis to produce gametes

Pituitary Gland not affecting other glands meloncyte stimulating hormone (MSH) skin color changes prolactin (PRL) milk production carbohydrate / fat metabolism growth hormone skeletal and muscular growth increases the rate of amino acids entering cells to produce proteins

Anterior pituitary function Pituitary Gland Anterior pituitary function

Hypothalamus and pituitary Pituitary Gland Hypothalamus and pituitary

Hormones Classified as protein or protein derivative bind to receptor on cell membrane steroid receptors are located within the cytoplasm of the cell react with receptor site on selected cells secreted by endocrine glands, endocrine cells, and certain neurons travel through the bloodstream to nonadjacent target cells chemical signal communication between cells, body parts

Hormones prostaglandins local hormone not carried by blood affects neighboring cells promotes pain and inflammation growth hormones promotes cell division

Hormones pheromones affect metabolism influence the behavior of another individual active between animals not humans

Hormone Action activation of receptor transduction of signal functional response

Action of Hormones wide range of effects induce target cells 2 ways hormones can influence cell metabolism 1.) peptide hormone peptides, proteins, glycoproteins, modified amino acids Glucagon, ADH, oxytocin, TRH, insulin, somatotropin, prolactin, FSH, LH, TSH

Mechanism of a peptide hormone Protein Hormone Mechanism of a peptide hormone

Protein Hormone hormone binds to a receptor at cell surface glucagon hormone binds to a receptor at cell surface binding triggers a change in activity of enzymes inside the cell glucagon receptor cyclic AMP + Pi ATP cAMP activates protein kinase A Protein kinase A converts phosphorylase kinase to active form and inhibits an enzyme required for glucagon synthesis.

Action of Hormones 2.) steroid hormone act more slowly action lasts longer limited to adrenal cortex, ovaries and testis Estrogens, progestins, androgens, cortisol, aldosterone derived from cholesterol enters the cell because they are lipids binds with DNA activates transcription inhibits transcription

Mechanism of a steroid hormone Steroid Hormones Mechanism of a steroid hormone

Major Endocrine Glands and Their Hormones Hypothalamus Pituitary gland Anterior pituitary Pineal gland Melatonin Posterior pituitary Oxytocin Vasopressin (antidiuretic hormone, ADH) Thyroid gland Thyroid hormone (T3 and T4) Calcitonin Adrenal glands (atop kidneys) Parathyroid glands Parathyroid hormone (PTH) Adrenal medulla Epinephrine and norepinephrine Ovaries (in females) Estrogens Progestins Figure 32.11a Exploring the human endocrine system (part 1: glands and hormones) Adrenal cortex Glucocorticoids Mineralocorticoids Testes (in males) Androgens Pancreas Insulin Glucagon 32

Thyroid Gland epiglottis thyroid cartilage (Adam’s apple) pharynx trachea (windpipe) parathyroid gland anterior posterior

Stimulus Response Blood level of thyroid hormone falls below a set point. + Hypothalamus – TRH – Anterior Pituitary Rise in the blood level of thyroid hormone inhibits secretion of TRH and TSH. TSH Thyroid Gland Thyroid hormone is secreted

Thyroid/Parathyroid located in the neck largest gland stimulates all cells to metabolize faster more glucose broken down, more energy used contains triiodthyronine (T3) / thyroxine (T4) regulates metabolism and growth rate

Thyroid/Parathyroid lack of iodine can result in a simple goiter hypothyrodism minimal production cretinism failure of thyroid to develop properly results in stunted growth myxedema adults lethargy, weight gain, loss of hair, slower pulse rate, lowered body temperature

Thyroid/Parathyroid hyperthyroidism overproduction exophthalmic goiter eyes protrude due to swelling of the muscles that moves the eyes

Parathyroid hormone action Parathyroid Gland Parathyroid hormone action

Calcium Regulation calcium levels high calcitonin regulates calcium levels in the blood secreted by thyroid gland in response to high levels causes calcium to be deposited in the bone tissue osteoblasts reduces the activity and number of osteoclasts cell that causes the erosion of bone

Calcium Regulation parathyroid glands calcium levels too low PTH released in response to low calcium levels promotes the activity of osteoclasts promotes the reabsorption of calcium by the kidneys activates vitamin D stimulates the absorption of Ca from the intestine

Calcium Regulation hyperparathyrodism Ca levels too high results in tetany body shakes from continuous muscle contractions brought about by increased excitability of nerves hypoparathyrodism Ca levels too low bones become soft and fragile

Adrenal Glands sit atop the kidneys consists of adrenal medulla inner portion produces epinephrine and norepinephrin brings about bodily changes emergency responsible for fight-flight response to stress and excitement effects are short term

Same receptors but different intracellular proteins (not shown) Different receptors Different cellular responses Different cellular responses Epinephrine Epinephrine Epinephrine  receptor  receptor  receptor Glycogen deposits Figure 32.13 One hormone, different effects Vessel dilates. Vessel constricts. Glycogen breaks down and glucose is released from cell. (a) Liver cell (b) Skeletal muscle blood vessel (c) Intestinal blood vessel 46

Adrenal Glands adrenal cortex outer portion secretes cortisol maintains glucose levels in the absence of food inhibits blood glucose uptake by muscle and other tissues causes breakdown of proteins to amino acids and conversion to glucose causes degradation of adipose tissue to fatty acids for use as energy source

Adrenal Glands feedback control of cortisol secretion hypothalamus senses rise in glucose and secretes less releasing hormone (CRH) corticotropin-releasing hormone anterior pituitary responds by secreting less ACTH adrenocorticotropic hormone adrenal cortex slows its secretion of cortisol

Control of cortisol secretion Adrenal Cortex Control of cortisol secretion

Adrenal Glands mineralocorticoids regulate salt and water balance leads to an increase in blood volume and blood pressure

Control of Glucose Metabolism Hormones and glucose metabolism

Pancreatic Hormones lies between the kidney and near the duodenum secretes insulin high blood glucose (sugar) stimulates uptake of glucose by liver cells adipose cells muscle cells stored as glycogen lowers blood sugar

Pancreatic Hormones glucagon low blood glucose major target are the liver and adipose tissue stimulates liver to break down glycogen uses fat and protein in preference to glucose as energy adipose tissue cells break down fat to glycerol and fatty acids liver then takes these up and uses them as substrates for glucose formation

Excess glucose accumulates Diabetes Mellitus Excess glucose accumulates Type 2 target cells don’t respond usually appears in adults diet, drugs Type 1 autoimmune disease usually appears in childhood insulin injections

Hormones in the Balance Impacts, Issues Video Hormones in the Balance