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Chapter 42 Animal Hormones. Biology 102 Tri-County Technical College Pendleton, SC. Two Major Systems. Nervous system involved with high-speed messages Estes and the Dutch Oven…oh yeah!!!! Endocrine system is much slower and involves production, release, and movement of chemical messages

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Chapter 42 animal hormones

Chapter 42 Animal Hormones

Biology 102

Tri-County Technical College

Pendleton, SC

Two major systems
Two Major Systems

  • Nervous system involved with high-speed messages

    • Estes and the Dutch Oven…oh yeah!!!!

  • Endocrine system is much slower and involves production, release, and movement of chemical messages

  • As always, it is the subtle interplay between the two systems that COUNTS…

Endocrine system components
Endocrine System Components

  • Most endocrine glands/tissue contain neurosecretory cells that secrete hormones

    • Chemical signal that communicates regulatory messages within body

  • Hormones reach all parts of body but only certain types of cells [target cells] are equipped to respond

  • Only target cells respond because ONLY they have receptors for that hormone

Insect development hormones
Insect Development Hormones

  • In insects/crustaceans, molting triggered by ecdysone

    • Secreted (insects) by prothoracic glands just behind head

    • Favors development of adult characteristics

    • i.e., from caterpillar to butterfly

  • Ecdysone production in insects controlled by brain hormone (BH)

  • Balanced by juvenile hormone (JH) secreted by corpora allata (pair of small glands just behind brain)

  • Promotes retention of larval characteristics

General chemical classes
General Chemical Classes

  • Peptide hormones: oxytocin, ADH, calcitonin, PTH, and thymosin

  • Protein hormones: GH, prolactin, insulin, and glucagon

  • Glycoprotein hormones: FSH, LH, TSH

  • Amine hormones: T3 and T4, epinephrine and norepinephrine, and melatonin

  • Steroid hormones: glucocorticoids, mineralocorticoids, androgens, estrogens, and pregesterone

Two general classes
Two General Classes

  • Hormones can be divided into two general classes: steroid and nonsteroid

  • Nonsteroid hormones such as amines, peptides, and proteins usually combine with receptors in target cell membrane

    • First messenger/second messenger

    • Signal transduction pathway: converts extracellular chemical signal to specific intracellular response

Classes cont
Classes, cont.

  • Steroid hormones are lipid-soluble and easily diffuse into cells

  • Once inside target cell, steroid hormone MAY combine with specific protein molecules (the receptor[s]) or they may exert their influence directly

  • Typically, steroid hormone bind with their specific protein receptor

Stirring the steroids
Stirring the Steroids…

  • Steroids easily cross plasma membrane

  • Binding of steroid (signal molecule) with specific receptor (usually in nucleus) initiates signal transduction process

  • Signal initiates cascade of events in which proteins interact with other proteins until final response(s) are achieved

  • In many cases, signal-receptor complex binds to DNA to modify gene expression

Target cell specificity
Target Cell Specificity

  • Each chemical signal has specific shape recognized by that signal’s target cells

  • Signal’s action begins when it binds to specific receptor

  • Receptor protein may be in PM of target cell or inside the cell

  • Diversity of responses of target cells depends on nature of target cell and the affinity of receptor molecules on or within cell

  • Cells are unresponsive to signal if they lack appropriate receptors


  • Hypothalamus is region of lower brain

  • Hormone releasing cells are 2 sets of neurosecretory cells whose secretions are stored in posterior pituitary (antidiuretic hormone/oxytocin)

  • Hormones released into capillaries in region at base of hypothalamus

  • Capillaries drain into portal vessels (short blood vessels that subdivide into second capillary bed within anterior pituitary

Hypothalamus cont
Hypothalamus, cont.

  • Hypothalamic hormones have direct access to gland they control (releasing/release-inhibiting hormones)

Pituitary location function
Pituitary: Location/Function

  • Pituitary located at base of hypothalamus

  • Has 2 discrete parts that develop from 2 separate regions of embryo and have very different functions

  • Anterior pituitary (adenohypophysis) consists of endocrine cells that synthesize and secrete several hormones directly into blood

Pituitary cont
Pituitary, cont.

  • Posterior pituitary (neurohypophysis) is extension of the brain

  • Stores and secretes 2 hormones made by hypothalamus

  • Oxytocin: contraction of uterus and mammary gland cells; regulated by nervous system

  • Antidiuretic hormone (ADH): promotes water retention by kidneys; regulated by water/salt balance

Adh homeostasis neg fb
ADH/Homeostasis/Neg. FB

  • Osmoreceptors in hypothalamus monitor blood osmolarity

  • Plasma osmolarity >s; osmoreceptors shrink slightly and transmit nerve impulse to certain hypothalamic neurosecretory cells

  • These cells respond by releasing ADH into general circulation from their tips in posterior pituitary

  • Target cells for ADH are cells lining collecting ducts of nephrons in the kidneys

Adh cont
ADH, cont.

  • ADH binds to receptors on target-cells and activates signal-transduction pathway that increases water permeability of collecting ducts

  • Water retention is >ed as water exist collecting ducts and enters nearby capillaries

  • Osmoreceptors also simulate thirst drive

Adh iii

  • As more dilute blood (lower osmolarity) arrives at brain, hypothalamus responds by reducing ADH secretion and lowering thirst sensation

  • This prevents overcompensation by stopping hormone secretion and quenching thirst

  • This negative feedback scheme includes hormonal action and behavioral response

Tropic hormones
Tropic Hormones

  • Have other endocrine glands as their targets

  • Four of hormones secreted by anterior pituitary gland are tropic hormones

  • Thyroid-stimulating hormone (TSH)) stimulates thyroid gland

  • Adrenocorticotropic hormone (ACTH) stimulates adrenal cortex to secrete glucocorticoids

Tropic hormones cont
Tropic Hormones, cont.

  • Follicle-stimulating hormone (FSH) stimulates production of ova and sperm

  • Luteinizing hormone (LH) stimulates ovaries and testes

  • Anterior pituitary also secretes other hormones with profound effects on body: Growth hormone (GH), Prolactin; Melanocyte-stimulating hormone; Endorphins and enkephalins

Control of anterior pituitary
Control of Anterior Pituitary

  • Neurosecretory cells in hypothalamus exert control over anterior pituitary by secreting 2 kinds of hormones into blood

  • Releasing hormones: anterior pituitary secretes its hormones

  • Inhibiting hormones: make A.P. stop secreting hormones

  • Is subtle blend of R and I hormones that control timing and amount of hormonal release by A.P.

Thyroid gland
Thyroid Gland

  • In humans/other mammals, thyroid gland consists of 2 lobes located on ventral side of trachea

  • Produces 2 very similar hormones from tyrosine

    • Triiodothyronine (T3) and Tetraiodothyronine (T4)/thyroxine

  • In mammals, T3 is more active form

Thyroid cont
Thyroid, cont.

  • Thyroid important in human development

  • Deficiency (cretinism) results in markedly retarded skeletal growth/poor mental development

  • Thyroid hormones important for normal functioning of bone-forming cells and for branching nerve cells during embryonic development of the brain

  • In adults, help maintain normal BP, heart rate, muscle tone, digestion, and reproductive functions

Thyroid iii
Thyroid III

  • Hyperthyroidism (> amounts) produces high body temperature, profuse sweating, weight loss, irritability, and high BP

  • Hypothyroidism (< amounts) produces cretinism in infants and symptoms of weight gain, lethargy, and intolerance to cold in adults

Thyroid iv
Thyroid IV

  • Deficiency of iodine in diet can lead to shortage of thyroid hormones and cause enlargement of thyroid called a goiter

  • Thyroid also produces calcitonin which lowers calcium levels in blood as part of calcium homeostasis

    • Stimulates osteoblasts to use circulating calcium to deposit new bone

Thyroid hormones loop
Thyroid Hormones Loop

  • HypothalamusTRH (thyroid releasing hormone) [some texts call thyrotropin-releasing hormone or TRH] to anterior pituitaryTSH (thyroid stimulating hormone)induces thyroid to manufacture and release T3 and T4

  • Increasing levels of TSH, T3, and T4 signal hypothalamus to reduce secretion of TRH

Parathyroid glands
Parathyroid Glands

  • Four parathyroid glands embedded in surface of thyroid

  • Function in homeostasis of calcium ions

  • Parathyroids secrete parathyroid hormone (PTH)

  • Raises blood levels of calcium [has opposite effect of thyroid hormone calcitonin

Parathyroids cont
Parathyroids, cont.

  • Stimulates Ca2+ reabsorption in kidneys and induces osteoclasts to decompose mineralized matrix of bone and release Ca2+ into blood

  • Vitamin D (synthesized in skin) essential to PTH function

  • Lack of PTH causes blood levels of calcium to drop dramatically

  • Leads to convulsive contractions of skeletal muscles

  • If unchecked, tetany follows which is FATAL!!!


  • Pancreas has both endocrine and exocrine functions

  • Islets of Langerhans are cluster of endocrine tissue in the pancreas which secretes 2 hormones directly into circulatory system

  • Alpha (α) cells secrete peptide hormone called glucagon

  • Beta (β) cells secrete the hormone insulin

Hormones of pancreas
Hormones of Pancreas

  • Glucagon and insulin work together (antagonistic) to regulate [ ] of glucose in blood

  • In humans, blood glucose levels must remain about 90 mg/100 mL for proper body functioning

  • At glucose levels above set point, insulin secreted and lowers blood glucose [ ] by stimulating body cells to take up glucose from blood

Pancreas iii
Pancreas III

  • Insulin also slows glycogen breakdown in liver and inhibits conversion of AAs/fatty acids to sugar

  • Blood glucose levels drop below set point, glucagon is secreted and increases blood glucose [ ] by stimulating liver to increase hydrolysis of glycogen, convert AAs/Fas to glucose, and slowly release glucose into blood

Adrenal medulla
Adrenal Medulla

  • Adrenal medulla synthesizes/secretes catecholamines (epinephrine and norepinephrine)

  • Secreted in times of stress

  • Nerve cells excited by stressful stimuli release neurotransmitter acetylcholine in medulla

  • Acetylcholine combines with cell receptors and stimulates release of epinephrine

  • Norepinephrine released independently of epinephrine

Adrenal medulla cont
Adrenal Medulla, cont.

  • Have rapid/dramatic effect on several targets

  • Glucose mobilized in skeletal muscle cells

  • Fatty acid released from fat cells

  • Rate and stroke of heartbeat increased

  • Delivery of blood changed

  • Oxygen delivery to body cells increased

Adrenal cortex
Adrenal Cortex

  • Adrenal cortex synthesizes and secretes corticosteroids

  • Stressful stimuli cause hypothalamus to secrete releasing hormone that stimulates release of ACTH from anterior pituitary

  • ACTH stimulates release of corticosteriods from adrenal cortex

  • In humans, 2 primary types are glucocorticoids (cortisol) and mineralocorticoids (aldosterone)

Adrenal cortex cont
Adrenal Cortex, cont.

  • Glucocorticoids promote glucose synthesis from noncarbohydrate substances such as proteins

  • Also have immunosuppressive effects and are used to treat inflammation

  • Mineralocorticoids affect salt and water balance

  • Aldosteone stimulates kidneys to reabsorb sodium ioins and water from filtrate

Adrenal cortex iii
Adrenal Cortex III

  • Glucocorticoids/mineralocorticoids important to maintaining body homeostasis during extended periods of stress

  • Short-term stress responses triggers release of epinephrine and norepinephrine (fight or flight)

  • Long-term stress responses trigger the release of mineralocorticoids and glucocorticoids

Gonadal hormones
Gonadal Hormones

  • In humans, gonads are ovaries and testes

  • Hormones are androgens, estrogens, and progestins

  • Primary androgen is testosterone

  • Primary estrogen is estradiol

  • Progestins include progesterone

Gonadal hormones cont
Gonadal Hormones, cont.

  • Gonadotropins from anterior pituitary (FSH and LH) control synthesis of both androgens and estrogens

  • FSH and LH controlled by gonadotropin-releasing hormone (GnRH) from hypothalamus

Wrapping it up so to speak
Wrapping it up…so to speak

  • Pineal gland is small mass of tissue near center of mammalian brain

  • It secretes melatonin which regulates functions related to light and to seasons marked by changes in day length (biorhythms)

  • Pineal contains light sensitive cells or has nervous connections from the eyes (depends on species)

  • Some studies indicate it has role in fertility

Wrapping cont
Wrapping, cont.

  • Thymus is located just posterior to sternum

  • Produces thymosin

  • Promotes development and maturation of lymphocytes

  • Important in immunity

  • Larger and most active in younger years, by adulthood, has atrophied and is mostly just gone….as is this chapter…