The Endocrine System

Endocrine system

Consists of ductless endocrine glands scattered throughout the body, that for the most part is not connected anatomically

Function of the endocrine system

Secreting hormones in the blood

Why can only a specific target cells can respond to each hormone

Only target cells have the receptors required for the binding with particular hormone

Hormone

A stimulant or chemical messenger, secreted by the endocrine glands

Example of excitatory hormone

Growth hormone

Example of inhibitory hormones

Somatostatin

Which hormones does somatostatin inhibits

The growth hormone

Function of hormones

1. Regulate the body’s internal environment in accordance with internal changes and external environment fluctuations

2. Controls the regeneration and maintenance of the tissues

Regulatory chemical messengers in the body

1. Endocrine hormones

2. Neurohormones

3. Neurotransmitters

4. Parahormones

5. Autocrone hormones

6. Pheromones

Endocrine hormones

Carried by the blood circulation

Neurohormones

Directly as a message or signal from the CNS to the endocrine system, in addition to the hormones circulating within the hypophyseal portal system (between the hypothalamus and the pituitary gland )

Neurotransmitters

Secreted by the terminal branches of the nerve axon, exert their in the area of the synapses, and their effect ends at the site where they are produced ; serotonin. They do not enter the bloodstream, with the exception of those secreted by the neuroendocrine system; adrenaline

Parahormones

Do not enter the bloodstream stream at all but pass through the interacellular fluid

Autocrine hormones

Bound to receptor in the same cell that produces them

Pheromones

Airborne and exert an effect on the olfactory receptors of animals

Chemical classification of hormones

1. Peptides and proteins hormones

2. Steroid hormones

3. Amino-Acid derived hormones

4. Glycoprotein

Peptide and Protein Hormones

Large group that covers the majority of hormones such as Peptide: Vasopressin and Protein: prolactin

Steroid hormones

Lipid derived from cholesterol-like sex hormones (testosterone, progesterone, and cortisol)

Amino Acid - Derived Hormones

derived from the amino acid tyrosine and tryptophan, such as Epinephrine and norepinephrine

Glycoprotein

Protein bound to one or more carbohydrate group, such as FSH and LH

Kind of biochemical receptors

1. External fixed receptors

2. Internal mobile receptors

3. Internal nuclear receptors

External fixed receptors

Proteins are found on the surface of the plasma membrane

External fixed receptors Breakdown

Protein hormones and catecholamines

Internal mobile receptors

In the cytoplasm, it breaks down steroid hormones

Internal nuclear receptors

On the nucleus, causes the breakdown of thyroid hormones

The hormones on the hypothalamus gland

Releasing and inhibiting hormones ( somatostatin and dopamine)

Target cells of somatostatin and dopamine

Anterior pituitary

Major function of somatostatin and dopamine

Control release of anterior pituitary hormones

Hormones of the posterior pituitary

1. Vasopressin (antidiuretic hormone, ADH)

2. Oxytocin

Target cells of Vasopressin (antidiuretic hormone, ADH)

Kidney tubules And Arterioles

Major functions of Vasopressin (antidiuretic hormone, ADH) in the Kidney tubules

Increases H2O reabsorption

Major functions of Vasopressin (antidiuretic hormone, ADH) in the Arterioles

Produces Vasoconstriction

Target cells of oxytocin

1. Uterus

2. Mammary glands

Major function of oxytocin in uterus

Increase contractility

Major function of oxytocin in mammary glands

Cause milk ejection

Hormones of the anterior pituitary

1. Thyroid - stimulating hormone (TSH)

2. Adrenocorticotropic hormones (ACTH)

3. Growth hormone (GH)

4. Follicle - stimulating hormone (FSH)

5. Luteinizing hormone (LH)

6. Prolactin (PRL)

Target cells of Thyroid - stimulating hormone (TSH)

Thyroid follicular cells

Major function of Thyroid - stimulating hormone (TSH)

Stimulates T3 and T4 secretion

Target cells of Adrenocorticotropic hormone (ACTH)

Zona fasciculata and zona reticularis of the adrenal cortex

Major function of Adrenocorticotropic hormone (ACTH)

Stimulates cortisol secretion

Target cells of Growth hormone (GH)

Bone and soft tissue and the liver

Major function of growth hormone in the bone and soft tissue

Essential but not solely responsible for growth and exerts metabolic effects by means of IGF-I , indirectly stimulate growth of bones and soft tissue; directly stimulate protein synthesis

Major function of Growth hormone in the liver

Stimulates IGF-I secretion

Target cells of Follicle - stimulating hormone (FSH)

1. Females : ovarian follicles

2. Males : seminiferous tubules in testes

Major function of Follicle - stimulating hormone (FSH) in females

Promotes follicular growth and development; stimulates estrogen secretion

Major function of Follicle - stimulating hormone (FSH) in male

Stimulates sperm production

Target cells of Luteinizing hormone (LH)

1. Females : Ovarian follicle and corpus luteum

2. Males : Interstitial cells of Leydig in testes

Major function of Luteinizing hormone (LH) in females

Stimulates ovulation, corpus luteum development, and estrogen and progesterone secretion

Major function of Luteinizing hormone (LH) in males

Stimulates testosterone secretion

Target cells of Prolactin (PRL)

1. Females : Mammary glands

2. Males: Unknown

Major function of Prolactin (PRL) in females

Promotes breast development and stimulates milk secretion

Major function of Prolactin (PRL) in males

Uncertain

Hormones of Pineal gland

Melatonin

Target cells of Melatonin

Brain, anterior pituitary, reproductive organs , etc

Major function of Melatonin

Entrains body’s biological rhythm with external cues; inhibits gonadotropins; its reduction likely inhibits puberty; acts as an antioxidant

Hormone of Thyroid gland follicular cells

Tetraidothyronine (T4, thyroxine) ( T3 tri-iodothyronine)

Target cells of Tetraidothyronine

Most cells

Major function of Tetraidothyronine

Increases metabolic rate; is essential for normal growth and nerve development

Hormone of Thyroid gland C cells

Calcitonin

Target cells of Calcitonin

Bone

Major function of Calcitonin

Decreases plasma Ca 2+ concentration

Hormone of Parathyroid gland

Parathyroid hormone (PTH)

Target cells of Parathyroid hormone (PTH)

Bone, Kindneys, and intestine

Major function of Parathyroid hormone (PTH)

Increase plasma Ca2+ and decreases plasma PO3- concentration; stimulates vitamin D activation

Hormones of the Adrenal cortex

1. Aldosterone (mineralocorticoid)

2. Cortisol (glucocorticoid)

Target cells of Aldosterone (mineralocorticoid)

Kidney tubules

Manor functions of Aldosterone (mineralocorticoid)

Increases Na+ reabsorption and K+ secretion

Target cells of Cortisol (glucocorticoid)

Most cells

Major function of Cortisol (glucocorticoid)

Increase blood glucose at the expense of protein and fat stores; contributes to stress adaptation

Hormones of Adrenal medulla

Epinephrine and Norepinephrine

Target cells of Epinephrine and Norepinephrine

Sympathetic receptor sites throughout the body

Major function of Epinephrine and Norepinephrine

Reinforce sympathetic nervous system; contribute to stress adaptation and blood pressure regulation

Hormones of Endocrine pancreas (islets of Langerhans)

1. Insulin (B cells)

2. Glucagon (a cells)

Target cell for insulin and glucagon

Most cells

Major functions of Insulin

Promotes cellular uptake, use, and storage of absorbed nutrients

Major function of Glucagon

Is important for maintaining nutrient levels in blood during the postabsorptive state

Hormones of the Females gonads : Ovaries

1. Estrogen

2. Progesterone

Target cell of estrogen

1. Female sex organs

2. Bone

Major function of Estrogen in the female sex organs

Promotes follicular development; governs development of female secondary sexual characteristics; stimulates uterine and breast growth

Major function of Estrogen in the bone

Enhance pubertal growth spurt; promotes closure of the epiphyseal plate

Target cell of progesterone

Uterus

Major function of progesterone

Prepare for pregnancy

Hormones of Male gonads : Testes

Testosterone

Target cells of Testosterone

1. Male sex organs

2. Bone

Major function of Testosterone in the male sex organs

Stimulates sperm production; governs development of male secondary sexual characteristics; promotes sex drive

Major function of testosterone in the bone

Enhances pubertal growth spurt; promotes closure of the epiphyseal plate

Hormones of Testes and Ovaries

Inhibin

Target cells of Inhibin

Anterior pituitary

Major function of Inhibin

Inhibits secretion of FSH

Hormones of Placenta

1. Estrogen and Progesterone

2. Human chorionic gonadotropim (hCG)

Target cells of Human chorionic gonadotropim (hCG)

Ovarian corpus luteum

Major function of Human chorionic gonadotropim (hCG)

Maintain corpus luteum of pregnancy

Hormones of the Digestive tract

Gastrin, secretin, cholecystokinin

Target of Gastrin, secretin, cholecystokinin

Stomach p, pancreas, gallbladder

Primary action of Gastrin, secretin, cholecystokinin

Stimulates activities of the stomach, pancreas and gallbladder

Hormones of the kidney

Erythropoietin

Target of Erythropoietin

Bone marrow

Primary actions of Erythropoietin

Stimulates red blood cell production

Hormones of the kidney and liver

Renin-angiotensin

Target of Renin-angiotensin

Adrenal cortex, blood vessels