Endocrine System

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Unit- 4

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Endocrine System

• The coordination of various body functions with the help of certain chemicals.

• These chemicals are known as hormones.

• Hormones in simple term are non nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

• The neural system and the endocrine system jointly coordinate and regulate the physiological functions in the body.

• Father of Endocrinology is Thomas Addison

• First hormone was discovered by Stanley.

• Largest endocrine organ is Gut.

• The endocrine glands and hormones producing diffused tissues/cells located in different parts of our body.

• Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads.

• In addition to these gastrointestinal tract, liver, kidney, heart also produce hormones.

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Functions of the Endocrine System:

• Controls the processes involved in movement and physiological equilibrium

• Includes all tissues or glands that secrete hormones into the blood

• Secretion of most hormones is regulated by a negative feedback system

• The number of receptors for a specific hormone can be altered to meet the body’s

demand

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Chemical Classificaton of Hormones

• Steroid Hormones:

• Lipid soluble

• Diffuse through cell membranes

• Endocrine organs

• Adrenal cortex

• Ovaries

• Testes

• placenta

• Nonsteroid Hormones:

• Not lipid soluble

• Received by receptors external to the cell membrane

• Endocrine organs

• Thyroid gland

• Parathyroid gland

• Adrenal medulla

• Pituitary gland

• pancreas

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Hormone Actions

• Steroid Hormones

• Pass through the cell membrane

• Binds to specific receptors

• Then enters the nucleus to bind with the cells DNA which then activates certain genes (Direct gene activation).

• mRNA is synthesized in the nucleus and enters the cytoplasm and promotes protein synthesis for:

• Enzymes as catalysts

• Tissue growth and repair

• Regulate enzyme function

• Nonsteroid Hormones

• React with specific receptors outside the cell

• This triggers an enzyme reaction with lead to the formation of a second messenger (cAMP).

• cAMP can produce specific intracellular functions:

• Activates cell enzymes

• Change in membrane permeability

• Promote protein synthesis

• Change in cell metabolism

• Stimulation of cell secretions

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Control of Hormone Release

• Negative feedback mechanism- hormone release is triggered by stimulus, rising levels of hormone inhibit further release

• Endocrine stimuli-

• Hormonal- hormones stimulate the release of others

• Humoral- blood stimulates release of hormones

• Neural- nerves stimulate hormone release

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Anterior Pituitary Gland

• Growth Hormone (GH)- affects growth of skeletal muscles and bones

• Prolactin (PRL)- stimulates milk production after pregnancy

• Gonadotropic- regulates hormone activity of sex organs

• Also effects adrenal cortex and thyroid hormone release

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Posterior Pituitary

• Oxytocin- helps during pregnancy

• Antidiuretic hormone (ADH)- inhibits urine production

• Alcohol inhibits ADH causing increased

output of urine

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Thyroid Gland

• Thyroid hormone

• Controls the rate at which glucose is “burned”

• Calcitonin

• Decreases calcium levels in

blood deposits on bone

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Parathyroid Gland

• Parathyroid hormone (PTH)- regulates Ca2+ in blood

• If Ca2+ level drops bones is

broken down

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Adrenal Gland

• Adrenal Cortex

• Releases hormones that regulate mineral content in blood

• Adrenal Medulla

• Produces epinephrine and norepinephrine

• Helps with stressful situations

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Pancreas

• Insulin- increases glucose uptake into cells and stores in liver

• Glucagon- stimulates

breakdown of glucose stores

in the liver

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Pineal Gland

• Melatonin

• Establishes body’s day/ night cycle

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Thymus

• Thymosin

• “Programs” T cells

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Gonads

• Androgens (male)- sperm formation, development of male char

• Estrogens (female)- development of female char

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Reproductive System

Female Reproductive Organs

• External parts: vulva, which includes the labia, clitoris and urethra, Vaginal Orifice

• Internal Parts: The Vagina, Cervix, the uterus, which hosts the developing

fetus, produces uterine secretions, and passes the male's sperm through

to the fallopian tubes; and the ovaries, which produce the female's egg

cells.

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Vagina:

• The vagina is attached to the uterus through the cervix.

• Fibro-muscular tubular tract leading from the uterus

Cervix

• The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina.

• It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall.

• The cervix is also named the neck of the uterus.

Uterus

• The uterus is a hollow muscular pear- shaped organ

• It lies in the pelvic cavity between the bladder and rectum

• Measure: 7.5 cms long, 5cm wide and walls are 2.5 cms long

• Weighs 30-40gms

• Parts: Fundus, Body and Cervix, Supporting ligaments

• Layers: Perimetrium, Myometrium and endometrium

• Function: Menstrual Cycle, Acceptance of fertilized egg, embedding the embryo in the endometrium, mechanical protection, nutritional support, and waste removal for the developing embryo (weeks 1 to 8) and fetus (from week 9 until the delivery),contractions in the muscular wall of the uterus are important in pushing out the fetus at the time of birth.

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Fallopian tube

• The Fallopian tubes or oviducts are two tubes leading from the ovaries of female mammals into the uterus.

• On maturity of an ovum, the follicle and the ovary's wall rupture, allowing the ovum to escape and enter the Fallopian tube.

Ovaries

• The ovaries are female gonads( glands producing sex hormones and the ova) .

• Measurements: 2.5 to 3.5 cms log, 2cm wide and 1 cm thick

• They are paired organs that are located near the lateral walls of the pelvic cavity.

• These organs are responsible for the production of the ova and the secretion of hormones ( Estrogen, HCG, Progesterone) .

• The process by which the ovum is released is called ovulation.

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• The male reproductive system consists of a number of sex organs that form a part of the human reproductive process. In humans, these sex organs are located outside the body, around the pelvic region.

• The main male sex organs are

the penis and the testicles which produce semen and sperm, and a system of ducts

(including the epididymis, dutus vas deferens, ejaculatory duct and urethra) and accessory glands and several supporting structure

Male Reproductive Organs

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External genital organs

Penis

• The penis is the male copulatory organ. It has a long shaft and an enlarged bulbous-shaped tip called the glans penis.

Scrotum

• The scrotum is a pouch-like structure that hangs behind /under the penis. It holds and protects the testes. It also contains numerous nerves and blood vessels.

Internal Genital Organs

Testes

• Paired oval glands in the scrotum measuring about 5cms long and2.5cms in diameter

• Weight: 10-15gms

• Develop around kidneys and travel down through inguinal canal and situate in the scrotum

• Sperm cells or Spermatozoa are produced, developed and mature in the testes (spermatogenesis)

• They secrete hormone: Testesteron

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Epididymis

• The epididymis, a whitish mass of tightly coiled tubes cupped against the testicles, acts as a maturation and storage for sperm before they pass into the vas deferens, that carry sperm to the ampullary gland and prostatic ducts.

Vas deferens

• The vas deferens, also known as the sperm duct, is a thin tube approximately 30 centimeters (0.98 ft) long that starts from the epididymis to the pelvic cavity.