Endocrine System PDF

The Endocrine system They secrete hormones directly to the blood& include: -The pituitary gland. - Thyroid gland - Suprarenal gland The Pituitary Gland  The Pituitary Gland Has anterior and posterior lobes. The Anterior lobe (consists of: -pars distalis -pars intermedia -pars tu...

The Endocrine system They secrete hormones directly to the blood& include: -The pituitary gland. - Thyroid gland - Suprarenal gland The Pituitary Gland  The Pituitary Gland Has anterior and posterior lobes. The Anterior lobe (consists of: -pars distalis -pars intermedia -pars tuberalis The Posterior lobe (neurohypophysis): -pars nervosa  Pars Distalis It is surrounded by a thin C.T. capsule. It consists of irregular cords of cells. Numerous fenestrated capillaries are present between the cells. Cells of Pars Distalis Chromophobes Chromophils More numerous (52%) Less numerous (48%) dont take histological stain take histological stain smaller Larger non granular cytoplasm Have granular cytoplasm  Chromophils Acidophil cells Basophil cells (37%) (11%) Moderate in size Larger in size Have acidophilic granules Have basophilic granules Somatotrophs Growth Thyrotrophs: Thyroid Hormone (GH) Stimulating Hormone (TSH) Lactotrophs prolactin Gonadotrophs: Follicle Stimulating Hormone (FSH) & Luteinizing Hormone (LH) Corticotrophs: Adrenocorticotrophic Hormone (ACTH)  Pars intermedia - Separated from pars distalis by thin incomplete cleft. - Cells arranged in follicles or cords with blood vesseles in between  Pars Nervosa 1- It is lightly stained because it is formed of a very few number of cells and mainly nerve fibers. Nerve fibers carry the neurosecretory material from the hypothalamic nuclei. Neurosecretions (vassopressin and oxytocin) are stored in dilatations along the nerve fibers known as Herring bodies. 2- Few number of cells “pituicytes”: are neuroglial cells. 3- Rich blood capillaries. The Pituitary Gland  Thyroid gland The gland is surrounded by a C.T. capsule which sends septa to divide the gland into indistinct lobules. The parenchyma is formed of follicles. The follicles are filled with acidophilic colloid. Lining epithelium varies from flat to columnar. Two types of cells are present: Follicular cells and C cells Blood capillaries are found between the follicles. Follicular cells (principal cells) Parafollicular cells (C. cells) main type of cells secrete thyrocalcitonin hormone secrete thyroid hormones (T3 & (lowers blood calcium level) T4). - Cuboidal, Columnar or Squamous Larger in size Lie on a basement membrane. They are present between the The apical portions of the cells follicular cells and basement reach the follicular cavity. membrane They have central rounded nuclei (don’t reach the follicular cavity.) and basophilic cytoplasm. Their cytoplasm is lightly stained. The suprarenal glands Each gland has an outer cortex and an inner medulla The adrenal cortex 1- Zona glomerulosa: a narrow zone under the capsule. It is formed of columnar acidophilic cells with few lipid droplets arranged in arched groups (glomeruli) separated by blood capillaries. The cells secrete mineralocorticoids (aldosterone). 2- Zona fasciculata: It is the middle zone. It consists of large polyhedral cells with acidophilic vacuolated cytoplasm which contains numerous lipid droplets. They are arranged in columns and separated by blood capillaries. The cells secrete glucocorticoid 3- Zona reticularis: The cells are small polyhedral with less vacuolated cytoplasm. They are arranged in anastomosing cords separated by blood capillaries. The cells secrete sex hormones and some glucocorticoids.  Adrenal Medulla It is composed of two types of cells separated by wide blood capillaries: 1- Chromaffin cells: have basophilic cytoplasm. The cells secrete catecholamines “epinephrine and norepinephrine”. 2- Ganglionic cells regulate the process of secretion of catecholamines