THE ENDOCRINE SYSTEMTHE ENDOCRINE SYSTEM

Like the Nervous System, the Endocrine System work through a group of chemical messengers. The endocrine messengers are called hormones.

Hormones: Substances secreted by one group of cells that travel through the blood stream and regulate the metabolic functions of other cells.

Hormones can affect only cells that have receptors that can bind the hormone

Target cells: Those cell types that can be affected by a given hormone

FUNCTIONS OF THE ENDOCRINE SYSTEM

The Endocrine system helps to maintain homeostasis by coordinating and regulating the activities of cells, tissues, organs, and systems throughout the body

The Endocrine System helps to control and integrate:

1- Reproduction

2- Growth

3- Development

4- Defense against stress

5- Water, electrolyte and nutrient balance

6- Energy balance

7- Cellular metabolism

Homeostasis

It is the ability of the human body to maintain relatively stable internal conditions (temperature, PH, etc) even though the outside world changes continuously.

A good homeostasis is indispensable to maintain the organism in good health. Most diseases can be regarded as a result of disturbance of homeostasis.

Example: The body temperature must be near to 37 C (98.6 F). When temperature increases only three degrees (to 40 C), the organism is in danger.

o

o

o

Temperature: - 20 C Temperature: + 50 C o o

Homeostatic Control Mechanisms maintain the temperature of the bodies near to 37 C, and both men are in good health

o

F E E D B A C K S Y S T E M S

Causes the variable to change in a direction opposite to that of the initial change.

Causes the variable to accelerate the change in the same direction that the initial disturbance.

1- Negative feedback mechanisms:

2- Positive feedback mechanisms:

or

or

[Calcium] in blood

Parathyroid hormone is released by parathyroid gland

Stimulates the osteoclasts to resorb bone, releasing calcium to the blood

First Hormonal Mechanism

Second Hormonal Mechanism

Calcitonin hormone is released by thyroid gland

Inhibits osteoclasts to resorb bone, and encourages calcium salt deposit in bone matrix

[Calcium] in blood

[Calcium] in blood

[Calcium] in blood

1- ENDOCRINE SYSTEM IN NEGATIVE FEEDBACK MECHANISMS

SENSOR

EFFECTOR

HYPOTALAMUS

CONTROL CENTER

Example:

PITUITARY GLAND

Positive feedback mechanisms are used to amplify or perpetuate events. They are referred as “cascades”.

2- ENDOCRINE SYSTEM IN POSITIVE FEEDBACK MECHANISMS

Uterine contractions

OXYTOXIN

Neural

electrical

impulses

DELIVERY!

Hypothalamus

Control of Hormone Secretion

Most of hormone secretions are controlled by the Hypothalamus and the Pituitary gland

Pituitary gland

Corpus callosum Septum pellucidum Fornix

Pineal gland

Anterior commissure

Thalamus

Intermediate mass

Hypothalamus Mamillary bodyOptic chiasm

Pituitary gland

Epi- thalamus

Three mechanisms of Hypothalamic Control over Endocrine Function

TSH, FSH, LH, ACTH, GH, PRL,

MSHOxytoxin and Antidiuretic Hormone (ADH)

Posterior lobeAnterior lobe

melanocyte stimulating

hormone

Hormones produced by the Anterior Lobe or Adenohypophysis (1)

2

1

5

Hormones produced by the Anterior Lobe or Adenohypophysis (2)

melanocyte stimulating hormone

4

3

3

6

GONADOTROPINS

Hormones produced by the Hypothalamus and released by the posterior pituitary

Hormonal Control of Water Retention in the Body

The body controls how much water is either sent to the bladder (in urine) or retained in circulation through a hormone called “antidiuretic hormone” (ADH)

When the body needs water, receptors in the hypothalamus sense the increase of solute concentration in the blood, and the hypothalamus orders the release of ADH from the pituitary gland.

ADH works on the distal nephron tubule and the collecting duct increasing their permeability to water. Consequently, more water moves out of the nephron tubule and collecting duct and thus back into circulation

Hormonal Control of Water Retention in the Body

SENSOR

EFFECTOR

HYPOTALAMUS

CONTROL CENTER

PITUITARY GLAND

Uterine contractions

OXYTOXIN

Neural

electrical

impulses

DELIVERY!

The Thyroid Gland

Right lobe

Left lobe

Isthmus

T4 or Thyroxine

T3 or Triiodothyronine

Calcitonin

Thyroid Hormones

1- T4 or thyroxine

2- T3 or triioodothyronine

Follicular hormones (they are produced by the follicular cells)

1- They increase the rate of oxygen uptake and the basal metabolic rate

2- They enhance the effects of sympathetic stimulation (increasing heart rate, blood pressure, nervousness, and sweating)

3- They help to maintain body temperature

4- They help to regulate growth, development, and intracellular metabolism by increasing protein synthesis and lipid breakdown

5- They stimulate RBC formation, and speed up bone turnover

1- T4 or thyroxine

2- T3 or triiodothyronine

3- Calcitonin

3- Calcitonin

It is released in response to high levels of calcium in the blood

Calcitonin hormone is released by thyroid gland

Inhibits osteoclasts to resorb bone, and encourages calcium salt deposit in bone matrix

[Calcium] in blood

[Calcium] in blood

The Parathyroid Glands

Thyroid gland, posterior view

Parathyroid glands

Parathyroid glands

The Parathyroid Hormone

It increases calcium blood levels by targeting bone and kidneys

1- In bones

[Calcium] in blood

Parathyroid hormone is released by parathyroid gland

Stimulates the osteoclasts to resorb bone, releasing calcium to the blood

[Calcium] in blood

2- In kidneys

- It increases calcium reabsortion

- It increases formation and secretion of calcitriol Increases absorption of calcium and

phosphate from the intestines

Adrenal or Suprarenal Glands

Mineralocorticoids(Aldosterone)

Glucocorticoids(Cortisol, Cortisone and

Corticosterone)

Sex hormones( androgens)

Medulla (It is considered part of Sympathetic Autonomic nervous System)

Catecholamines(Epinephrine and Norepinephrine)

Hormones of the Adrenal Glands

1- Mineralocorticoides (Aldosterone)

-It increases sodium ion and water reabsortion in kidneys

-It increases potassium secretion in kidneys

Aldosterone secretion is regulated by the renin-angiotencin mechanism

Blood pressure or plasma solute concentration

Renin-angiotencin mechanism

Aldosterone secretion

2- Glucocorticoids (Corticosterone and Cortisol)

-They help the body to resist stressors

-They depress the immune system and the inflammatory response

3- Gonadocorticoids or Sex Hormones (Androgens)

-They are masculinizing hormones.

- In females they stimulate sexual drive. After menopause they are converted to estrogens.

4- Catecholamines (Epinephrine and Norepinephrine)

-Blood glucose levelsThey increase:-Cardiac activity -Blood pressure-Glycogen breakdown-Triglyceride breakdown

Three mechanisms of Hypothalamic Control over Endocrine Function

The Pancreas

Endocrine pancreas Exocrine pancreas

Pancreatic acini

They secrete large quantities of an alkaline, enzyme rich fluid

Islets of Langerhans

1- Beta cells:

2- Alpha cells:

3- Delta cells:

4- F cells:

Insulin

Glucagon

Somatostatin

Pancreatic polypeptide

1- Glucagon (Released by alpha cells)

-It stimulates the liver to produce glucose

-It stimulates to breakdown glycogen

Glucose in blood Glucagon

(Alpha cells)

Pancreas Liver Glycogen

Glucose

2- Insulin (Released by beta cells)

- High blood glucose

- Parasympathetic stimulation

- High level of some aminoacids

(Beta cells)Pancreas

Insulin

- It increases the rate of glucose uptake by cells

- It increases cellular metabolism

- It increases the storage of lipid and glycogen

- Increases aminoacids absorption and protein synthesis

Seminiferous tube

Primary spermatocyte

Secondary spermatocyte

Spermatids

Sperm (immature)

Spermatogonia

Interstitial or Leydig cells: Produce androgens

(testosterone)

The Gonads

Sustentacular or Sertoli cells: Produce Inhibin

The Development of the Egg

Primary Primary oocytesoocytes

Primary Primary folliclesfollicles

Secondary Secondary folliclesfollicles

Tertiary Tertiary folliclesfollicles

Corpus Corpus luteum luteum ::

FolliclesFollicles: Estrogens and Inhibin

Progesterone

The Pineal Gland

Melatonin:

Pineal gland

1- Inhibiting reproductive functions

2- Protecting against damage for free radicals

3- Setting circadian rhythms

Hormones of the Kidneys

1- Calcitriol:

It stimulates uptake of calcium and phosphate ions from the gut

2- Erythropoietin:

It stimulates the production of red blood cells by red bone marrow

3- Renin:

It converts angiotensinogen into angiotensin-I and starts the cascade of enzymatic changes known as the renin-angiotensin system

Atrial Natriuretic Peptide (ANP)It is produced by the atrial cells of the heart

It reduces the blood volume and blood pressure