Animal Physiology Exam 2

Classic non-neural endocrine

Hormones are released into the blood and exert actions at distant site

Neuroendocrine

Hormones are released by neural cells into the blood and exert actions at distant sites

Paracrine

Hormones diffuse to a target cell located in proximity (neighboring cells)

Autocrine

Hormones affect secreting cell itself 

Hormone secretion

What is the primary role of the “classic” endocrine glands?

Pancreas

Exocrine digestive enzymes + endocrine islets

Gonads

Gamete production + sex steroids (testosterone + estrogen)

Stomach / intestine

Digestion + gastrointestinal hormones (gastrin, CCK)

Liver

Metabolism + insulin-like growth factor I (IGF-I)

Adipose tissue

Energy storage + leptin (regulates appetite, energy balance)

Peptide Hormones

Most hormones. Short chains of amino acids. Ex: insulin and hypothalamic hormones

Steroids

Hormones derived from cholesterol. Ex: Adrenal and gonadal hormones

Amino acid derivatives

Hormones derived from amino acids. Ex: thyroid hormones and catecholamines

1. DNA transcribed to mRNA

2. Translation of mRNA into pre-hormone (an inactive precursor)

3. Pre-hormone processed in ER and Golgi —→ Prohormone ——> Hormone

4. Hormone is packaged in vesicles and stored in the cytoplasm

5. Secretion occurs (specific stimulus required)

6. Hormone transported and dissolved in blood

Describe the steps of synthesis, storage, and release of a peptide hormone.

1. Requires series of enzymatic reactions 

2. Different types of steroidogenic cells have different sets of enzymes, therefore they have different end products 

3. Hormones are not stored; diffuse out of cell and are transported bound to plasma protein

Describe the synthesis and secretion of steroid hormones

Surface receptors (extracellular / membrane R) as they cannot pass through the hydrophobic lipid bilayer

Peptide hormones and amines bind to?

1. Ligand binds receptor

2. G protein is activated

3. Second messenger produced (cAMP, cGMP, IP3/DAG, Ca2+)

4. Cellular response

Explain G protein-linked receptors

(For majority of hormones)

1. Ligand 

2. Intrinsic tyrosine kinase auto phosphorylates

3. Recruits intracellular signaling proteins 

4. Triggers metabolic or gene expression responses 

Explain Enzyme-linked receptors (catalytic R)(For Insulin + Growth Factor)

1. Steroid hormones are lipophilic and diffuse across the cell membrane

2. Hormone binds to intracellular receptors (cytoplasm or nucleus)

3. Hormone bindings causes receptor conformational changes and activation

4. Activated receptors bind to hormone response element (HRE)

5. Hormone receptor complex acts as a transcription factor which regulates gene expression

6. Synthesized protein results in physiological response

Explain how steroid hormones bind to intracellular hormone receptors (how steroid hormones act)

Negative Feedback

Most hormone secretion results in what kind of feedback?

High blood glucose —→ increases insulin —→ lowers glucose

Give an example of negative feedback

hormone concentrations; hypothalamus-pituitary 

Hormone Mediated feedback is controlled by _______ and involves the ________ axis.

Hypothalamus

Secretes releasing hormones

Pituitary

Secreted tropic hormones

Rhythmic basis

Many hormones are secreted on a?

light-sensitive retinal 

Neural input is generated from specialized _________ cells.

The superchiasmatic nucleus (SCN) and further to the hypothalamic releasing hormone-secreting neurons

Signals from neural input are sent to?

The circadian rhythm

SCN neurons impose a daily rhythm called?

melatonin; pineal gland

In addition to the circadian rhythm, the SCN regulates ______ secretion for the _______.

Upregulation

More receptors result in increased sensitivity. Ex: prolactin increases the number of receptors in the mammary gland

Downregulation

Fewer receptors result in decreased sensitivity. Ex: when this process occurs, insulin receptors become less sensitive and high insulin levels prolong.

Additive effect

Combined effect equals the sum of individual effects

Synergism

Combined effect greater than sum of individual effects

Permissiveness

One hormone is required for another to exert the full effect

Antagonism

One hormone opposes the effect of another

Hypothalamus

The base of the brain that contains several nuclei (groups of cell bodies of neurons)

Pituitary stalk

The pituitary (hypophysis) is connected to the hypothalamus by the?

Posterior lobe (neurohypophysis) + Anterior lobe (adenohypophysis)

Name the lobes of the pituitary

Intermediate lobe; MSH

In some animals a third pituitary lobe called ________ is present and secretes _____.

Vasopressin + Oxytocin (peptide hormones)

What hormones are released from the posterior pituitary?

Vasopressin (VP)

Anti-Diuretic Hormone (ADH) that increases reabsorption of H2O by kidneys and increases vasoconstriction. Released by the posterior pituitary.

Oxytocin (OC)

Released during uterine contraction during childbirth and results in milk ejection during breast feeding. Released by the posterior pituitary.

ADH

Increases water reabsorption in kidneys

Thyrotropin (TSH), Adrenocorticotropin (ACTH), Growth hormone, Gonadotropins (LH + FSH), MSH (in some animals), and Prolactin

Which hormones are released from the anterior pituitary?

Posterior pituitary is a neural extension of the hypothalamus composed of axons of hypothalamic neurons. Hormones are produced by Paraventricular nucleus (PVN) and Supraoptic nucleus (SON). Hormones travel down the axon where they are stored in axon terminals in the posterior pituitary

Describe the hypothalamic control of the Posterior pituitary.

No direct nervous connection between anterior pituitary and hypothalamus. Hypothalamic hormones are released in hypothalamic capillaries where they enter the hypothalamic-hypophyseal portal system. The portal system controls the release of pituitary hormones in blood. Releases hormones and inhibiting hormones.

Describe the hypothalamic control of the Anterior pituitary.

Thyrotropin-Releasing Hormone (TRH)

Stimulates thyroid hormone secretion (T3/T4); Thyrotroph —→ TSH

Corticotropin-Releasing Hormone (CRH)

Stimulates cortisol secretion from the adrenal cortex

Corticotroph ——> ACTH

Growth Hormone-Releasing Hormone (GHRH)

Stimulates growth hormone release

Somatotroph —→ GH

Somatostatin (GHIH)

Inhibits GH and TSH release 

Somatotroph —→ GH

Thyrotroph ——→ TSH

Gonadotropin-Releasing Hormone (GnRH)

Stimulates sex hormone production and gametogenesis

Gonadotroph —→ LH, FSH

Prolactin-Releasing Hormone (PRH) (ex: TRH)

Stimulates prolactin secretion

Lactotroph ——> PRL

Prolactin-Inhibiting Hormone (PIH / Dopamine)

Inhibits prolactin secretion

Lactotroph ——→ PRL

IGF-1

GH does not directly cause growth. Instead, growth-promoting effects are largely mediated by _____ which stimulates the growth of soft tissues and bones.

Spherical follicles

What is the thyroid composed of?

Follicular cells; colloid-filled space

Each follicle of the thyroid is lined by a single layer of secretory epithelial cells called ________ around a _________.

Thyroxine (T4) + Triiodothyronine (T3)

Follicular cells synthesize?

Thyroglobulin

A large protein with tyrosine residues, secreted by follicular cells in the colloid. Used to produce thyroid hormones

Iodination

Tyrosine residues on Thyroglobulin are iodinated which forms monoiodotyrosine (MIT) or diiodotyrosine (DIT)

Coupling

MIT and DIT are combined, forming T3 or T4 which remains attached to TG

T4 (inactivated form)

90% of thyroid hormones are secreted as?

1. Increase basal metabolic rate (BMR)

2. Increase oxygen consumption and energy expenditure in most tissues

3. Increase heat production 

4. Increase glycolysis and gluconeogenesis

5. Increase lipolysis

6. Maintains normal excitability, reflexes, and alertness

7. Essential for normal growth in children; critical for brain development during fetal and postnatal life

What are the actions of thyroid hormones?

Metamorphosis (in fish and amphibians) and migratory behavior and adaptive osmoregulatory changes in salmonids

What is the action of thyroid hormone in lower vertebrates?

Hypothyroidism

A TH deficiency which causes developmental cretinism (stunted growth and impaired CNS development) and slows growth, lowers metabolism, causes fatigue, cold intolerance, and weight gain in adults and children

Goiter

A thyroid enlargement caused by either hypothyroid or hyperthyroid disorder

Hypothyroid goiter

A goiter resulting from TH deficiency. Ex: Iodine deficiency or Hashimoto’s thyroidits

Hyperthyroid goiter

A goiter resulting from TH excess. Ex: Grave’s disease

From sun exposure or from diet via absorption by the small intestin

Where do you get vitamin D from?

Cholecalciferol

D3 (animals)

Ergocalciferol

D2 (plants)

Ultraviolet (UV) light

D3 is synthesized from dehydrocholesterol in the skin and requires?

Liver: Vitamin D converted to 25(OH)-D

Kidney: 25(OH)-D converted to 1,25 (OH)2-D

What two reactions activate vitamin D (which is inactive on its own)?

Vitamin D and Parathyroid hormone (PTH)

What two things regulate calcium?

Regulates Ca metabolism. Stimulus is decreased calcium levels, action is to increase calcium levels. 

What does the Parathyroid hormone do?

1. Kidney: Increases calcium reabsorption and increases the production of active vitamin D

   1. Bone: Bone resorption increases calcium in the blood

How does the parathyroid hormone (PTH) increase Ca levels?

Calcitonin

Decreases bone resorption by decreases osteoclast activity, and further decreasing calcium levels. Also results in small decrease in renal calcium reabsorption

Adrenal Gland Medulla

Secreted catecholamines (Epinephrine + norepinephrine) stimulated by the sympathetic system (stress).

Catecholamines (epinephrine +norepinephrine)

Released by the adrenal gland medulla; reinforces the “fight-or-flight” response; increases heart rate and blood glucose levels

Adrenal Gland Cortex

Secretes mineralocorticoids (aldosterone), glucocorticoids (cortisol), and androgens (with some estrogens)

Mineralocorticoids (Aldosterone)

Secreted by the adrenal gland cortex; regulates Na+ balance (in kidney ——> osmoregulation)

Glucocorticoids (cortisol)

Secreted by the adrenal gland cortex; regulates fuel metabolism; increases blood glucose levels and has anti-inflammatory and immunosuppressive effects

Androgens

Secreted by the adrenal gland cortex; mostly dehydroepiandrosterone (DHEA) and some estrogens

1. Glucose enters the B-cell (via facilitated diffusion via GLUT-2)

2. Glucose phosphorylated to G6P (glucose-6-phosphate)

3. Oxidation of G6P generates ATP

4. ATP closes ATP-sensitive K+ channels 

5. Depolarization opens voltage-gated Ca channels 

6. Ca enters the cell 

7. Exocytosis of insulin vesicles

Explain how insulin is released in the body.

Incretins

Hormones released by the digestive tract in response to food which increases insulin secretion

The gastrointestinal (digestive) tract (GIT)

Digestion occurs in?

Sphincters

The gastrointestinal tract is separated by muscular valves called?

Injestion

Getting food into the gastrointestinal tract (eating)

Mechanical digestion

The breakdown of food into small molecules by teeth (chewing) or stomach (churning)

Chemical digestion

The breakdown of food into small molecules by specific enzymes

Mouth and esophagus

The main parts of the body used in mechanical digestion (and some chemical)

Stomach

The organ that functions in digestion

Small intestine

The organ that functions in digestion and absorption

Large intestine

The organ that functions in the reabsorption of water during digestion

Carnivores: canines have pointed teeth for tearing

Herbivores: have incisors for cutting and molars for grinding

Filter feeders: Gill rakers and baleen plates

What are some adaptations of teeth?

Saliva

Produced by salivary glands in the mouth; lubricates food, digests polysaccharides, and has roles in taste and maintaining pH

Water (99%)

Electrolytes (Na+ and K+)

Mucin

Antibodies

Salivary amylase

What are the main components of saliva?

Mucin

A protein that forms thick, slimy mucus

Salivary amylase

Breaks down carbohydrates in the mouth

Esophagus

Secretes mucus and alternates contraction and relaxation of muscle along the side (peristalsis); moves food toward the stomach

Crop

A sac-like enlargement of the esophagus in birds that stores undigested food, have bacteria that aid in pre-digestion, and secretes “crop milk”