endocrine

• Endocrine system


  Consists of glands widely separated from each other with no physical connections
• Endocrine glands


  • Group of secretory cells surrounded by an extensive network of capillaries that facilitates diffusion of hormones from the secretory cells to the blood stream
  • Commonly referred as ductless glands

  
• In addition to the main endocrine glands, many other organs and tissues secrete hormones as a secondary function
• Example of organ secreting hormone as secondary function

  • Adipose tissue produces leptin which is involved in the regulation of appetite

  
• Some hormones such as prostaglandins do not travel to remote organs but act locally
• Endocrine Glands In Human Body

  • Pineal body
  • Pituitary gland
  • Thyroid gland
  • Parathyroid gland
  • Thymus gland
  • Adrenal gland
  • Pancreas
  • Ovaries in females
  • Testicles in males

  
• Hypothalamus and Pituitary Gland

  The pituitary gland and hypothalamus act as a unit, regulating the activity of most of the other endocrine glands

  
• Pituitary gland


  • Lies in the hypophyseal fossa of the sphenoid bone below the hypothalamus, to which it is attached by a stalk
  • Size of a pea, weighs about 500mg and consists of three distinct parts: Anterior pituitary gland (Adenohypophysis), Posterior pituitary gland (Neurohypophysis), Intermediate lobe

  
• Blood Supply: Hypothalamus and Pituitary Gland

  1. Arterial Blood: Supplied by branches from the internal carotid artery, anterior lobe is supplied indirectly, posterior lobe is supplied directly

  2. Venous Blood: Comes from both lobes, containing hormones, and leaves the gland in short veins that enter the venous sinus between the layers of dura matter

  
• Anterior Pituitary Gland


  • Supplied with arterial blood that has already passed through capillary bed in the hypothalamus
  • Hypothalamus and anterior pituitary are linked by a network of capillaries called the pituitary portal system

  
• Posterior Pituitary Gland


  • Formed from nervous tissue and consists of nerve cells surrounded by supporting glial cells called pituicytes
  • Neurons have their cell bodies in the supraoptic and paraventricular nuclei of the hypothalamus and their axon form a bundle known as hypothalamohypophyseal tract

  
• Thyroid Gland


  • Situated in the neck in front of the larynx and trachea at the level of the 5th, 6th and 7th cervical and 1st thoracic vertebrae
  • Highly vascular gland that weighs about 25g and is surrounded by a fibrous capsule
  • Resembles a butterfly in shape with two lobes on either side of the thyroid cartilage and upper cartilaginous rings of the trachea
  • Lobes are joined by a narrow isthmus, lying in front of the trachea
  • Lobes are roughly cone shaped, about 5cm long and 3cm wide
  • Two parathyroid glands lie against the posterior surface of each lobe and are sometimes embedded in thyroid tissue
  • Gland is composed of cuboidal epithelium that forms large spherical follicles
  • Between these follicles there are other cells found in a small groups: C cells, which secretes the hormone Calcitonin

  
• Blood and Nerve Supply: Thyroid Gland

  1. Arterial blood supply is through the superior and inferior thyroid arteries

  2. Superior thyroid artery is a branch of the external carotid artery and the inferior thyroid artery is a branch of subclavian artery

  3. Venous return is by the thyroid veins, which drains into the internal jugular veins

  4. Recurrent laryngeal nerve passes upwards close to the lobes of the gland and on the right side it lies near the inferior thyroid artery

  
• Parathyroid Gland


  • There are four small parathyroid glands, two embedded in the posterior surface of each lobe of the thyroid gland
  • Surrounded by fine connective tissue capsules
  • Cells forming the glands are spherical in shape and are arranged in columns with sinusoids containing blood between them

  
• Adrenal Gland


  • The two adrenal glands are located on the upper pole of each kidney enclosed within the renal fascia
  • About 4cm long and 3cm thick
  • Glands are composed of two parts: Outer part (Adrenal Cortex), Inner part (Adrenal Medulla)

  
• Blood and Nerve Supply: Adrenal Gland


  1. Arterial blood supply is by branches from the abdominal aorta and renal arteries

  2. Venous return is by suprarenal veins

  3. Right gland drains into the inferior vena cava and the left into the left renal vein

  
• Pancreatic Islets


  • The cells that made up the pancreatic islets (islets of Langerhans) are found in clusters irregularly distributed throughout the substance of pancreas
  • Three main cells in the islets: Alpha cells (secretes Glucagon), Beta cells (numerous, secretes Insulin), Delta cells (secretes Somatostatin)

  
• Pineal Gland


  • A small body attached to the roof of the third ventricle and is connected to it by a short stalk containing nerves, many of this terminate in the hypothalamus
  • 10mm long, reddish brown in color and surrounded by a capsule
  • Tends to atrophy after puberty and may become calcified in later life

  
• Organ


  • Hormone
  • Site of Action
  • Function
• Kidneys


  • Erythropoietin
  • Red Bone Marrow
  • Stimulation of RBC production
• Gastric Mucosa


  • Gastrin
  • Gastric glands
  • Stimulates secretion of gastric juice
• Intestinal Mucosa


  • Secretin
  • Stomach and Pancreas
  • Stimulates secretion of pancreatic juice, Slows stomach emptying
• Intestinal Mucosa


  • Cholecystokinin (CCK)
  • Gallbladder and Pancreas
  • Stimulates release of bile and pancreatic juice
• Adipose tissue


  • Leptin
  • Hypothalamus and other tissues
  • Provides feeling of fullness after eating
• Ovary and Testis


  • Inhibin
  • Anterior Pituitary
  • Inhibits secretion of FSH

  
• Heart (Atria)


  • Atrial Natriuretic Peptide (ANP)
  • Kidney tubules
  • Decrease sodium and water reabsorption in tubules
• Placenta


  • Human Chorionic Gonadotrophins (HCG)
  • Ovary
  • Stimulates secretion of female sex hormone during pregnancy
• Thymus


  • Thymosin
  • WBC (T Lymphocytes)
  • Development of T Lymphocytes