Chapter 16

Hormones produce one or more of the following cellular changes in target cells

1. Alter plasma membrane permeability- let things in and out of the cell that normally wouldn’t

2. Stimulate protein synthesis- indirectly or directly

3. Activate or deactivate enzyme systems- within the cell

4. Induce secretory activity- induce cells to secrete products.

5. Stimulate mitosis

• Endocrine system - the body's second controlling system which influences metabolic activities of cells by means of hormones

• Endocrine glands - pituitary, thyroid, parathyroid, adrenal, pineal, and thymus

• The pancreas and gonads produce both hormones and exocrine products

The hypothalamus has both neural functions and releases hormones

• Other tissues and organs that produce hormones - adipose cells, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart

• Hormones - chemical substances secreted by cells into the extracellular fluids and then enters bloodstream

• Regulate the metabolic function of other cells

• Have ling times ranging from seconds to hours

• Tend to have prolonged effects

• Amino acid based - most hormones belong to this class, including:

• Amines, thyroxine, peptide, and protein hormones

• Steroids - gonadal and adrenocortical hormones

Peptides are indirect through 2nd messengers within the cell, receptors are on the cell membrane, they bind to the cell receptor on the cell membrane and activate chemicals inside of the cell, known as second messengers. Can be transported directly into the blood because they are water soluble.

Steroids- direct means of action, receptors are in the nucleus, inside the cell. They can directly activate transcription and translation and start production of new chemicals and products inside the cell. To transport they have to be bound to a carrier protein in the blood.

Target cell activation depends on three factors

• Blood levels of the hormone- the more hormone you have in the blood, the more likely it is to activate the target cell.

• Relative number of receptors on the target cell-the more receptors you have, the more you can have the hormone bind to that target cell and activate it.

• The affinity of those receptors for the hormone-some receptors are able to bind the hormone better than others, depends on the person, genetics.

Up-regulation - target cells form more receptors in response to high levels of the hormone- as hormone levels get high, receptors increase on the target cell. Causing the target cell to be activated even more.

• Down-regulation - target cells lose receptors in response to high levels of the hormone-telling the target receptors on the target cell to decrease, decreasing the activity of the hormone.

• Concentrations of circulating hormone reflect:

• The more hormone in the blood, the more likely it is to have an effect.

• Rate of release- the faster you release it , the more you will have.

• Speed of inactivation and removal from the body-kidneys will remove hormone from the body in urine, enzymes will active them.

Hormones are removed from the blood by: Degrading enzymes, The kidneys, Liver enzyme systems.

• Three types of hormone interaction

• Permissiveness - one hormone cannot exert its

  effects without anther hormone being present-example: testosterone basically determines male characteristics. Estrogen is largely going to determine female characteristics. Both cannot have their effects unless thyroid hormone is present.

• Synergism - more than one hormone produces the

  same effects on a target cell- example:adrenaline will increase blood sugar levels in your body because your body needs it because it’s under stress. Glucagon also increases blood sugar levels in the body, so they have the same effect.

Antagonism - one or more hormones opposes the

action of anther hormone- example: insulin will lower blood sugar levels as opposed to glucagon. Example: parathyroid hormone increases blood calcium levels while calcitonin will decrease calcium levels.

Control of Hormone Release

• Blood levels of hormones:

• Are controlled by negative feedback systems

• Vary only within a narrow desirable range- normal range

• Hormones are synthesized/ made and released in response to:

1. Humoral,

2. Neural,

3. Hormonal stimuli

Humoral stimuli - secretion of hormones in direct response to changing blood levels of ions and nutrients. Hormones are secreted in response to changing blood levels of ions or nutrients. Example: insulin is released when blood sugar levels get high, in response to blood glucose, the nutrient.

• Neural stimuli - nerve fibers stimulate hormone release- example: the sympathetic nervous system which releases adrenaline or epinephrine is going to stimulate the adrenal gland to release more epinephrine into the blood. Once it gets to the blood, that hormone spreads throughout the whole body. The sympathetic nervous system isn’t just targeting one specific muscle or organ.

Hormonal stimuli- where one hormone stimulates the release of another hormone. The hypothalamus and pituitary gland operating under the hormonal stimuli. Example: the hypothalamus is going to stimulate the pituitary gland to release hormones. Example, hypothalamus is going to release TRH, thyrotropin releasing hormone, that stimulated the pituitary to release TSH, thyroid stimulating hormone. TSH goes to the thyroid and stimulates the thyroid to release thyroid hormone, T3 and T4.

Nervous System Modulation

• The nervous system can override normal endocrine controls

• For example, control of blood glucose levels

• Normally the endocrine system maintains blood glucose

• Under stress, the body needs more glucose, more energy.

• The hypothalamus and the sympathetic nervous system are activated to supply ample glucose, stimulate from the liver and release glucose in the blood.

Major Endocrine Organs: Pituitary (Hypophysis)

• Pituitary gland - two-lobed organ that secretes nine major hormones

• Neurohypophysis - posterior lobe (neural tissue) and the infundibulum- nervous tissue, connects directly to the hypothalamus through the infundibulum.Receives, stores, and releases hormones produced by the hypothalamus, does not produce any hormones itself. Example: receives and stores oxytocin and ADH from the hypothalamus and then release them into the blood.

Adenohypophysis - anterior lobe, made up of glandular tissue,Synthesizes and secretes a number of hormones, around 7 types of hormones.

Pituitary-Hypothalamic Relationships:

Posterior Lobe, neurohypophysis, basically an extension of the hypothalamus.

• The posterior lobe is a downgrowth of hypothalamic neural tissue

• Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract)

• Nuclei of the hypothalamus synthesize:

• Where Oxytocin and Antidiuretic hormone (ADH) is stored

• produced in the hypothalamus and then transported to the posterior lobe of the pituitary and released from there.

Pituitary-Hypothalamic Relationships:

Anterior Lobe

• The anterior lobe of the pituitary is an outpocketing of the oral mucosa "Rathke's Pouch"

• There is no direct neural contact with the hypothalamus

Pituitary-Hypothalamic Relationships:

Anterior Lobe

• There is a vascular connection, the hypophyseal portal system, consisting of:

• The primary capillary plexus

• The hypophyseal portal veins

• The secondary capillary plexus

Adenophypophyseal Hormones

• The six hormones of the adenohypophysis:

• Are abbreviated as GH, TSH, ACTH, ESH, LH, and PRL

• All controlled by the hypothalamus

Growth Hormone (GH)

GHRH and GHIH- releasing hormone stimulates the release of a growth hormone from the anterior pituitary, the inhibiting hormone is going to stop the release of growth hormone. Release is a positive effect, inhibit is a negative effect. Growth hormone stimulated muscle and bone growth and also has anti insulin like effects, raises blood sugar.

• Produced by:

• Somatotropic cells of the anterior lobe that:

Thyrotropin releasing hormone (TRH) and negative feedback

TRH causes the production of thyroid stimulating hormone. TSH will go to the thyroid to release T3 and T4, thyroid hormones. Controls your metabolism.

Thyroid Stimulating Hormone (Thyrotropin)(TSH)

• Produced by:

• Thyrotrope cells

• Function

• Tropic hormone that stimulates the normal development and secretory activity of the thyroid gland

• Regulation

• Triggered by hypothalamic peptide thyrotropin-releasing hormone (TRH)

• Negative Feedback - Rising blood levels of thyroid hormones act on the pituitary and hypothalamus to block the release of TSH

• When T3 and T4 get High, it feeds back to the hypothalamus cutting off TSH, TRH, T3 and T4- negative feedback.

Corticotropin releasing hormone (CRH)

Causes the release of that acth, that adrenocortocorticotropic hormone. ACTH is going to stimulate the adrenal gland to release cortisol, stress hormone.

Adrenocorticotropic Hormone (Corticotropin)(ACTH)

• Produced by:

• Corticotrope cells

• Function:

• Stimulates the adrenal cortex to release corticosteroids. steroid hormone. Stress is main reason that causes the release of CRH, ACTH and cortisol.

• Regulation:

• Triggered by hypothalamic corticotropin-releasing hormone
  (CRH) in a daily rhythm

• Negative feedback

• Internal and external factors such as fever, hypoglycemia, and stressors can trigger the release of CRH

GNRH and negative feedback

• Causes the production of follicle stimulating hormone and luteinizing hormone for females, stimulates egg and estrogen production . ICSH in males, stimulates sperm production. FSH in males and females. controls sex organs. Follicle refers to egg.

GNRH and positive feedback

• ICHS in males stimulates testosterone production. In females it stimulates estrogen production as well as ovulation.

Gonadotropins- sex hormones

• Produced by:

• Gonadotrope cells

• Functions:

• Regulate the function of the ovaries and testes

• FSH stimulates gamete (egg or sperm) production

Functions of Gonadotropins

• In females

• LH works with FSH to cause maturation of the ovarian follicle

• LH works alone to trigger ovulation (expulsion of the egg from the follicle

• LH promotes synthesis and release of estrogens and progesterone

Functions of Gonadotropins

• In males

• LH stimulates interstitial cells of the testes to produce testosterone

• LH is also referred to as interstitial cell-stimulating hormone (ICSH)

• Regulation:

• Triggered by the hypothalamic gonadotropin-releasing hormone (GnRH) during and after puberty

• when testosterone levels get high, it cuts off GNRH production. Negative feedback from gonadal hormones

Prolactin (PRL)

Produced by Lactotropes

• Functions

• In females, stimulates milk production by the breasts

• Regulation:

  • Triggered by the hypothalamic prolactin-releasing hormone (PRH)

  • Blood levels rise toward the end of pregnancy

  • Suckling stimulates PRH release and encourages continued milk production

  • Inhibited by prolactin-inhibiting hormone (PIH)

PRH and PIH

• Inhibiting hormones. Do not cause production of another hormone.

• Stimulate inhibit prolactin and prolactin stimulates milk production in females. In males, causes a calming effect after the child is born, can lower testosterone levels after a man has a child.

Activity of the Adenohypophysis

Stimulated the production of other hormones

• The tropic hormones (regulate the activity of other

• endocrine glands) that are released are:

• Thyroid-stimulating hormone (TSH)- T3 & T4

• Adrenocorticotropic hormone (ACTH)- Cortisol

• Follicle-stimulating hormone (FSH)- Testosterone

• Luteinizing hormone (LH)- Estrogen

The Posterior Pituitary and Hypothalamic

Hormones

Direct connection between the hypothalamus and the posterior pituitary. Hypothalamus produced ADH and oxytocin, antidiuretic hormone and oxytocin. Stored and released from the posterior pituitary.

• Posterior pituitary - made of axons of hypothalamic neurons, stores antidiuretic hormone (ADH) and oxytocın

• ADH and oxytocin are synthesized in the hypothalamus

Oxytocin

Causes uterine contractions and milk release, regulated by positive feedback.

• Functions:

• Oxytocin is a strong stimulant of uterine contraction

• Oxytocin triggers milk ejection ("letdown" reflex in women producing milk

• Regulated by:

• positive feedback mechanism to oxytocin in the blood

• This leads to increased intensity of uterine contractions, ending in birth

Hormone (ADH)

• Functions:

• ADH helps to avoid dehydration or water overload

• Prevents urine formation

• Regulated

• Osmoreceptors monitor the solute (salt) concentration of the blood

• With high solutes, ADH is synthesized and released, thus preserving water

• With low solutes, ADH is not released, thus causing water loss from the body

• Alcohol inhibits ADH release and causes copious urine output

Thyroid Gland

• The largest endocrine gland, located in the anterior neck, consists of two lateral lobes connected by a median tissue mass called the isthmus. H shape

• Composed of:

1. Follicle cells that produce Thyroid hormone

2. Parafollicular cells, produce the hormone calcitonin-important for regulation of calcium

Thyroid Hormone

• Thyroid hormone - the body's major metabolic hormone. Amino acid based but acts as a steroid, function of iodine.

• Consists of two closely related iodine-gontaining compounds

• T3- thyroxine;

• T4- triiodothyronine;

• TH Functions:

• Glucose oxidation, makes energy.

• Increasing metabolic rate, metabolism.

• Heat production

Effects of Thyroid Hormone

• Other TH Functions:

• Maintaining blood pressure

• Regulating tissue growth

• Developing skeletal and nervous systems

• Maturation and reproductive capabilities

Transport and Regulation of TH

• Regulation

• Mechanisms of activity are similar to steroids -they go through the cell membrane, they don’t bind receptors on the cell membrane. They activate the cell directly at the DNA activating transcription, translation. But they have to be transported bound to a protein.

• Regulation is by negative feedback

• Hypothalamic thyrotropin-releasing hormone
  (TRH) can overcome the negative feedback

Calcitonin

• A peptide hormone produced by the parafollicular, or C, cells

• Functions

• Lowers blood calcium levels

• Antagonist to parathyroid hormone (PTH)

Calcitonin

• Calcitonin targets the skeleton, where it:

Activates osteoblasts to take up bone and deposit bone. Blood levels lower by taking it out of the blood and putting it into the bone.

• Regulation

• Regulated by a humoral (calcium ion concentration in the blood) negative feedback mechanism

Parathyroid Glands

• Tiny glands embedded in the posterior aspect of the thyroid

• Cells are arranged in cords containing oxyphil and chief cells

• Produced by:

• Chief (principal) cells secrete PTH

• Functions:

• PTH (parathormone) regulates calcium balance in the blood- main calcium regulator for blood calcium levels, raises blood calcium levels when they start dropping.

Number of parathyroid glands varies, from 4-8

Effects of Parathyroid Hormone

• Functions:

PTH release increases Cat in the blood as it:

1. It activates osteoclasts in bone and breakdown bone releasing calcium into blood

2. Increase Calcium uptake from the food you eat by the small intestines

3. Increase reabsoprtion of calcium at the kidneys

• Regulation:

Rising Ca²+ in the blood inhibits PTH release

Adrenal (Suprarenal) Glands

• Adrenal glands - paired, pyramid-shaped organs atop the kidneys

• Structurally and functionally, they are two glands in

one

• Adrenal medulla (inner) - nervous tissue that acts as part of the SNS

• Adrenal cortex (outer) - glandular tissue derived from embryonic mesoderm

Adrenal Cortex

Synthesizes and releases steroid hormones called corticosteroids

• Produced by:

• Different corticosteroids are produced in each of the three layers

1. Zona glomerulosa (outside layer) - mineralocorticoids- minerals like sodium and potassium (chiefly aldosterone)

2. Zona fasciculata (middle layer) - glucocorticoids- glucose (chiefly cortisol)

3. Zona reticularis (inner layer) - gonadocorticoids (chiefly androgens)- testosterone

Mineralocorticoids

- Regulate the electrolyte concentrations of extracellular fluids- sodium and potassium balance. It will reabsorb sodium if sodium levels get low in the body to maintain sodium levels. If potassium levels start getting too high, it would cause secretion of potassium.

• Aldosterone - most important mineralocorticoid

• Functions:

• Maintains Na+balance by reducing excretion of sodium from the body

• Stimulates reabsorption of Na+ by the kidneys

Mineralocorticoids

• Regulation:

• Aldosterone secretion is stimulated by:

• Rising blood levels of K+, potassium

• Low blood Na+, sodium

• Decreasing blood volume or pressure- if sodium levels are low, it means sodium is lost through urine, losing water, decreasing blood volume. Aldosterone is released to absorb sodium and reabsorb water with it.

• If blood volume is dropping, blood pressure is dropping. Can be signs of low sodium.

Glucocorticoids (Cortisol)

Helps keep blood sugar levels up when stressed, metabolism is up.

• Help the body resist stress by:

• Keeping blood sugar levels relatively constant

• Maintaining blood volume and preventing water

• shift into tissue

• Functions:

• Cortisol provokes:

• Gluconeogenesis (formation of glucose from noncarbohydrates)- break down fats and then makes glucose.

• Rises in blood glucose, fatty acids, and amino acids

Excessive Levels of Glucocorticoids

• Excessive levels of glucocorticoids:

• Depress cartilage and bone formation

• Inhibit inflammation

• Depress the immune system

• Promote changes in cardiovascular, neural, and gastrointestinal function

Gonadocorticoids (Sex Hormones)

• Most gonadocorticoids secreted are androgens (male

• sex hormones), and the most important one is testosterone

• Functions:

• Androgens contribute to:

• The onset of puberty

• The appearance of secondary sex characteristics

• Sex drive in females

Adrenal Medulla

Innermost part of the adrenal gland, neural tissue.

• Produced by:

• Made up of chromaffin cells that secrete epinephrine and norepinephrine (sympathetic neurotransmitter/ hormones) common name is adrenaline.

• Function:

• Secretion of these hormones causes:

• Blood glucose levels to rise

• Blood vessels to constrict

• The heart to beat faster

• Blood to be diverted to the brain, heart, and skeletal muscle

Pancreas

• A triangular gland, which has both exocrine and endocrine cells, located behind the stomach, involved in a large part of digestion, releases digestive enzymes and alkaline or pancreatic juice that goes into the small intestine neutralizes the acid from the stomach.

• Produced by:

• Pancreatic islets (islets of Langerhans) produce hormones (endocrine products)- little clusters of cells that produce the hormones.

• The islets contain two major cell types:

• Alpha (a) cells that produce glucagon

• Beta (B) cells that produce insulin

• Pancreas is right below the stomach, left upper quadrant

Glucagon

• A 29-amino-acid polypeptide hormone that is a potent hyperglycemic agent. Acts through second messengers, transported freely in the blood.

• Functions:

• Its major target is the liver, where it promotes:

1. Glycogenolysis- breakdown of glycogen into glucose

2. Gluconeogenesis- production of glucose from lipids and proteins.

Stimulates the production of glucose, stimulates an increase in blood glucose.

Release of glucose to the blood from liver cells- directly from the liver to the blood.

All 3 increase blood glucose levels

Insulin

• Functions:

• Insulin:

• Lowers blood glucose levels by telling your cells to take out of the blood or tell your liver to take it out of the blood and store it as glycogen.

• Enhances transport of glucose into body cells

• Counters metabolic activity that would enhance blood glucose levels

• Every cell in the body needs glucose, especially neural cells.

Regulation of Blood Glucose Levels

• Regulation:

The hyperglycemic (high blood sugar) effects of glucagon and the hypoglycemic (Lowering blood sugar) effects of insulin.

Hypoglycemic effects of insulin- lowers blood sugar

Hyperglycemic effects of glucagon- raising blood sugar

Diabetes Mellitus (DM) (type 1 & 2)

• Results from hyposecretion or hypoactivity of insulin- usually a problem with the beta cells and pancreas

• The three cardinal signs of DM are:

• Polyurıa - excessive urination, too much glucose in the kidneys can’t be absorbed.

• Polydipsia- excessive thirst

• Polyphagia- excessive hunger

Gonads: Female

• Produced by:

• Paired ovaries in the abdominopelvic cavity produce estrogens and progesterone. Left and right lower quadrants.

• Functions:

• Maturation of the reproductive organs

• Appearance of secondary sexual characteristics

• Breast development and cyclic changes in the Uterine mucosa

Gonads: Male

• Produced by:

• Testes located in an extra-abdominal sac (scrotum) produce testosterone

• Functions:

• Initiates maturation of male reproductive organs

• Causes appearance of secondary sexual characteristics and sex drive

• Is necessary for sperm production

• Maintains organs in their functional state

Pineal Gland

• Small gland hanging from the roof of the third ventricle of the brain, in the epithalamus

• Secretory product is melatonin

• Functions:

• Melatonin is involved with:

• Day/night cycles

• Physiological processes that show rhythmic variations (body temperature, sleep, appetite)

Thymus

• Lobulated gland located deep to the sternum in the

• thorax

• Major hormonal products are thymopoietins and

• thymosins

• These hormones are essential for the development of

• the T lymphocytes (T cells) of the immune system

Gland Hormone Action

Pineal - melatonin - circadian rhythm

Anterior pituitary - GH - cell growth

Posterior pituitary - ADH - water balance

Thyroid - T3 & T4 - metabolism

Calcitonin - lowers blood Calcium

Parathyroid - PTH - Raises blood Calcium

pancreas - insulin - lowers blood sugar

Glucagon - raises blood sugar

Adrenal cortex - glucocorticoids - anti-inflammatory

Adrenal medulla - epinephrine - fight or flight

Ovaries - estrogen - female sex characteristics

Testes - testosterone - male sex characteristics