ENDOCRINE SYSTEM Exerts chemical control over the human body Maintains homeostasis Acts with nervous system to coordinate the body's activities Uses chemical messengers called hormones that are

transported by the circulatory system (blood)

TYPES OF HORMONES Steroid Amino acid Protein

HYPOTHALAMUS Inferior part of the diencephalon Control center of all autonomic regulatory activities of the

body Main function of the hypothalamus is homeostasis

o HOMEOSTASIS - maintaining the body’s internal environment

Plays a major role in controlling the secretions from the Pituitary gland

Sends neural and chemical signals to the pituitary gland

CHEMICAL SIGNALS1. Releasing Hormones

main purpose is to control the release of another hormone

Stimulates the release of hormones Capillary bed, portal vein, receptors.

2. Inhibitory Hormones inhibits release of hormones from another structure convey the hormones through the pituitary stalk into the

anterior pituitary.

*NEGATIVE FEEDBACK when the particular level of concentration of a particular

hormone reaches a certain level in the body, the endocrine gland that secreted the hormone in inhibited and the secretion of that hormone either ceases or decreases significantly

o helps to control the concentrations of a number of hormones in the body

PITUITARY GLAND (Hypophysis)

PITUITARY GLAND

• a pea-sized, compound endocrine gland, centrally located at the base of the brain.

• Sella turcica– saddle-shaped depression of the sphenoid bone where lies the pituitary gland

• A short stalk, the infundibulum, and a vascular network connect the pituitary gland to the hypothalamus.

• “master organs” of the ES (with the Hypothalamus)

2 FUNCTIONAL COMPONENTS

• Anterior Pituitary (Adenohypophysis)- The glandular epithelial tissue- The cells are organized in clumps and cords separated

by fenestrated sinusoidal capillaries.- Regulates other endocrine glands and some non-

endocrine tissueso 3 derivatives of Rathke’s pouch:

Pars distalis (distal lobe) Pars intermedia (intermediate lobe) Pars tuberalis (tuberal lobe)

• Posterior Pituitary (Neurohypophysis)- The neural (secretory) tissue- Presence of highly branched glial cells called

pituicytes that resemble astrocytes and are the most

abundant cell type in the posterior pituitary; serves a supporting role in the CNS

- NOT an endocrine gland; stores and releases secretory products from the hypothalamuso 3 components:

Neural lobe (Pars nervosa, Infundbular process)

Pituitary stalk (Infundibular stem) Median Eminence

*Hormones – See Hormones Page

THYROID GLAND

• Located in the anterior neck region adjacent to the larynx and trachea

• Consists of two lateral lobes united by an isthmus

• Composed of connective tissue septa and follicles

MAIN FUNCTION

• Synthesize the thyroid hormones - Thyroxine (Tetra – iodothyronine or T4)- Tri – iodothyronine (T3)- Calcitonin

STROMA

• Thin loose areolar connective tissue capsule that forms connective tissue septa

FOLLICULAR EPITHELIUM

• Surrounds each follicle

• Composed of reticular fibers and network of capillaries

• Can be simple squamous, cuboidal, or low columnar epithelium

THYROID FOLLICLE

• Structural unit of thyroid gland

• Roughly spherical cyst-like compartment

• Wall formed by follicular epithelium

• Central cavity contains a gelatinous substance called colloid

• Surrounded by 2 types of cells

a. Follicular cells- Also called Principal cells- Most numerous cell type- Cuboidal in shape with spherical nucleus- Secretion and synthesis of T3 and T4

b. Parafollicular cells - Also called C (clear) cells- Larger than follicular cells- Can occur either alone or in clumps- Synthesize and secrete calcitonin

THYROID HORMONES

1. Thyroxine (T4) and Tri – iodothyronine (T3)

• Responsible for growth,cell differentiation and control of the basal metabolic rate and oxygen consumption in cells

• Affect protein, lipid, and carbohydrate metabolism

2. Calcitonin

• Lower blood calcium levels through inhibition of bone resorption

• Secretion is triggered by elevation of blood calcium concentration

PARATHYROID GLAND

• Four small glands

• Usually embedded in the thyroid capsule

• Derived from the pharyngeal pouches

• Consists of 2 cell typesa. Chief Cells

- Synthesis and secretion of parathyroid hormone (parathormone)

b. Oxyphil Cells- Larger than chief cells- Found singly or in small groups - Less numerous than chief cells

PARATHYROID HORMONE ( Parathormone)

• Increases blood calcium

*See Hormones Page for additional information

ADRENAL GLAND

• Paired organs

• Flattened structure with half – moon shape

• Surrounded by dense irregular connective tissue – reticular fibers for support

• Embedded in adipose tissue

• 2 concentric layers:- Adrenal cortex- Adrenal medulla

• Cells of both layers are grouped in cords along capillaries

• Dense CT capsule sends thin septa to the interior of the gland – trabeculae

ADRENAL CORTEX

• Cells contain numerous lipid droplets

• Spongyocytes

• Cells that secrete glucocorticoids, mineralocorticoids, and gonadocorticoids

• Has 3 concentric layers with fenestrated capillaries

- Zona Glomarulosa Occupy 15% of the cortex Immediately beneath the capsule Columnar or pyramidal cells Arranged in closely packed, rounded, arched

cords, or small clumps Secrete hormone mineralocorticoid -

aldosterone

- Zona Fasciculata Occupy 65% of the cortex Intermediate zone Polyhedral, often binucleated cells with lipid

droplets in their cytoplasm Cells are also called spongyocytes due to

vacuolization Arranged in one or two – cell thick straight

cords Secrete hormone glucocorticoid - cortisol

- Zona Reticularis

Occupy 7% of the cortex Innermost layer – lies between zona

fasciculata and medulla Smaller cells disposed in irregular cords

forming an anastomosing network Presence of lipofuscin pigment granules –

large and numerous Irregularly shaped cells with pyknotic nuclei –

suggesting cell death Arranged in cords or clumps Secrete hormone sex hormones or

androgens

*GO FIND REX FOR A GOOD SEX*

*Hormones – see Hormones page

ADRENAL MEDULLA

• Lies in the center of the adrenal gland

• Composed of polyhedral cells

• Arranged in cords or clumps, supported by reticular fiber network

• Composed of chromaffin cells

• Secretes catecholamines – Epinephrine and Norepinephrine

• Contains sympathetic ganglion cells

Chromaffin Cells

• A neuroendocrine cell

• Release neurotransmitter into systemic circulation for systemic effects on multiple organs

• Contains NE and E cells- E cells

Characterized by containing small granules Store epinephrine

- NE cells Characterized by larger granules Contains dense cores giving an appearance

of eccentric “bulls - eyes” More intense chromaffin reaction Store norepinephrine

*Hormones – See Hormones Page

FEMALE REPRODUCTIVE SYSTEM

OVARIES

• Surface is covered by simple squamous or cuboidal epithelium called germinal epithelium

• Under the covered surface is the tunica albuginea made of dense irregular connective tissue and responsible for whitish color of ovary

• Below that tunica albuginea is the cortex of the ovary where there is predominance of ovarian follicles

• Deep in the cortex is highly vascularized connective tissue core of ovary, medulla

• Hormones: Estrogen and Progesterone

ESTROGEN

• Manufactured mostly in ovaries by developing egg follicles

• In addition, produced by the corpus luteum, placenta, liver, breasts and adrenal glands in smaller quantities

• Essential to the menstrual cycle

• Prepares uterus for pregnancy

• Enriching and thickening of endometrium

• Contributes to the development of secondary characteristics

• Breasts, widened pelvis, increased body fat in buttocks, thigh and hip region

• Less facial hair and smoother skin

• Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) help to control production of estrogen

PROGESTERONE

• Responsible for the changes in the endometrium in the second half of the menstrual cycle

• For fertility and pregnancy

• Prepare the endometrium for implantation of fertilized egg and its development

• Maintain the uterus throughout pregnancy

• Low progesterone hormones have negative influences on your body, fertility, pregnancy and can even lead to an expelling of a fertilized egg

EGG CELL

• The cell substance is known as the yolk or oöplasm

• The nucleus as the germinal vesicle and the nucleolus as the germinal spot

• The human ovum is surrounded by a number of egg envelopes:

- Vitelline membrane A thin, inner transparent layer secreted

by the ovum itself- Zona pellucid

A thick middle layer which is transparent and non - cellular

- Corona radiate An outer, thicker coat formed of radially

elongated follicular cells.

• Between the vitelline membrane and zona pellucida, there is a narrow space called perivitelline space

MALE REPRODUCTIVE SYSTEM

TESTES

• Located in the scrotum

• Secrete hormone known as androgen; most important of which is testosterone

• Have an exocrine part, Seminiferous tubules (tightly coiled) and endocrine part, intersitial or Leydig cells (clusters) Leydig cells

• Synthesise and secrete testosterone- Testosterone increases sharply at puberty- Essential for the production of sperm- Production of testosterone is controlled by the

release of luteinizing hormone (LH)

• Located in the interstitial tissue between the convuluted seminiferous tubules

• Occurs in clusters, which are variable in size and richly supplied by capillaries

• Its cytoplasm is strongly acidophilic and finely granular

• The nucleus is large, round and often located eccentric in the cell

GENERAL EFFECTS OF TESTOSTERONE

• Anabolic- Growth of muscle mass and strength- Increased bone density and strength- Linear growth- Bone maturation

• Androgenic (Virilizing)- Maturation of sex organs (part. Penis)- Formation of scrotum in the fetus - Deepening of voice (sec. sex charac.)- Growth of beard and axillary hair (sec. sex

charac.)

Hypothalamus

GnRH

Pituitary

LH

Testes

Testosterone

SERTOLI CELLS

• ‘Nurse’ cell of the testes

• Part of the seminiferous tubule

• Activated by follicle-stimulating hormone and has FSH-receptor on its membranes.

• Estradiol and Inhibin – hormone secreted- Estradiol

Prevent apoptosis (death of cells) of germ cells

- Inhibin Inhibit production of FSH

PINEAL GLAND

• Also called Epiphysis Cerebri

• A pine cone shaped gland

• Produces several important hormones including melatonin

• Melatonin influences sexual development and sleep-wake cycles

• Composed of cells called pinealocytes and cells of the nervous system called glial cells

• Connects the endocrine system with the nervous system in that it converts nerve signals from the sympathetic system of the peripheral nervous system into hormone signals

• Also contains sand - well - brain sand or corpora arenacea- Calcium-containing concretions in the pineal

parenchyma- Increase in size and number with age- Radio opaque- Provide a good midline-marker

• 2 cell types- Pinealocytes

95% of the cells Large, light and round nuclei Secretions: cocktail substances

May decrease secretory activity in most other endocrine glands

May delay puberty through antigonadotrophic effects

- Astrocytes Glial cells Dark, elongated nuclei

- Interstitial cells Greater number in the stalk of the gland Nuclei are elongated Stain more deeply than those of the

pinealocytes Resemble the astrocytes of the brain in

having long-cell process and an abundance of intermediate filaments throughout the cytoplasm

• The most prominent secretory product of the pineal body is melatonin

• Secretory activity in the pineal gland is stimulated by darkness and inhibited by light

MAIN FUNCTION

• Secretion of the hormone melatonin

• Regulation of endocrine functions

• Conversion of nervous system signals to endocrine signals

• Causes feeling of sleepiness

• Influences sexual development

PIA MATER

• The delicate inner layer of connective tissue that covers the brain

• Surrounding the pineal body

• Functions as its capsule and which sends connective tissue septa into the pineal body, subdividing it into lobules.

THYMUS GLAND

• Enclosed in a capsule and divided internally by cross-walls into many lobules (full of T-lymphocytes).

• Lymphocytes that have passed through the thymus are transformed into T cells.

• Lymphocytes are white blood cells that function to fight infection. There are two kinds of lymphocytes: B cells and T cells. T cells participate in identifying and destroying body cells that are infected.

HORMONES

• Thymosino Activates the immune system by activating the T-

Cells (T-Killer Cells; T-Helper Cells; T-Memory Cells)

• T – Lymphocyteso The thymus consists of lobules full of T-

lymphocytes (white blood cells associated with antibody production).

o T-lymphocytes migrate from the bone marrow to the thymus, where they mature and differentiate until activated by antigens.

ALIMENTARY SYSTEM

STOMACH

• Gastrino From G cellso Secretion of gastric acid by parietal cellso As stomach acidity increase, its production

decreases

• Ghrelino From P/D1 cellso Stimulate appetiteo Secretion of growth hormone from anterior

pituitary gland

• Somatostatino From D cellso Suppress release of gastrin, CCK, secretin o Reduces smooth muscle contractions

DUODENUM

• Ssecretino From S cellso Secretion of bicarbonate from liver, pancreas and

duodenal Brunner’s glando Enhances effects of CCKo Stops production of gastric juice

• Cholecystokenino From I cellso Release of digestive enzyme from pancreaso Release bile from gallbladder

LIVER

• Thrombopoietino From hepatocyteso Stimulates megakaryocytes to produce platelets

• Insulin Like Growth Factor (IGF)o From hepatocyteso Insulin like effectso Regulate cell growth and development

• Angiotensinogen and Angiotensino From hepatocyteso Vasoconstrictiono Release of aldosterone from adrenal cortex

dipsogen

PANCREAS

• Glucagono From α islet cellso Glycogenolysis and gluconeogenesis in livero Increases blood glucose level

• Insulino From β islet cellso Intake of glucoseo Glycogenesis and glycolysiso Lipid synthesis

• Somatostatino From δ islet cellso Inhibit release of insulino Inhibit release of glucagono Suppress the exocrine secretory action of

pancreas