Hypothalamus and Pituitary Gland

Hypothalamus

• Anterior end of diencephalon

• received signals from multiple sources in nervous system

  • concerned with wellbeing of body

• info used to cntrol secretion of pituiray ormones

Links between hypothalamus and pituirtay

1. direct vascular links to ANTERIOR→ hypothalamic hypophyseal portal system

   • special neurons synthesize and secrete releasing and inhibiting hormones

   • control secretion of anterior pituitray hormones

2. neural connections to POSTERIOR

Hypothalamic releasing and inhibitory hormones

1. Corticotrophin releasing hormone (CRH)

2. growth hormone releasing hormone (GHRH),

3. thyrotropin releasing hormone (TRH),

4. gonadotrophin releasing hormone (GnRH),

5. growth hormone release inhibiting hormone or somatostatin (SMS)

6. dopamine

Blood supply and relationship between hypothalamus and pit gland: human anterior pit

• stained with immunocytochemically

  • LM→ growth hormone cella and prolactin cells

    • enlarged prolactin cells in lactating women

  • EM-. ACTH and TSH cells

Anterior pituitary male rat

• Various endocrine cell types

• course of blood vessels passing through specimen

Rat Neurohypophysis

• shows pituicytes and axons

• notice:

  • difference between number and secretory granules in each of them

• Posterior pit→ composed of non-myellinated axons of neurons located in hypothalamus

  • axons contain numerous secretory granules

  • supported by glial cells→ pituicytes

  • numerous sinusoid capillaries present

Rat hypothalamus

• immunocytochemically stained for ADH and oxytocin

Pituitary gland (hypophysis) what it does

• secretes variety of hormones

• some regulate other endocrine glands

Where found and strucuture

• Beneath hypothalamus

Divided into two

1. Anterior (andenohypophysis)

   • contains intermdeiate lobe

     • well developed in certain mammals (not in humans)

2. Posterior (neurohypophysis) (pars nervosa)

Have different embryological origin

Hypothalamus and pituitary as a unit

• complex functional unit

• regulates

  • body growth

  • water metabolism

  • milk secretion

  • lactation

  • functions of

    • thyroid, adrenal and gonads

HYpothalamus is main regulator of pituitary secretions

Posterior vs Anterior connections with hypo

Posterior

• connected to hypo via pituitary stalk

• consists of axons from nerve cell bodies→ in hypothalamus

Anterior

• Mainly glandular epithelium

• intimate vascular connections with hypothalamus

Anterior pituitary structure

• consists of cords or clumps of cells

  • surrounded by sinusoid capillaries (S)

  • supported by network of collagen and reticulin fibres

• Due to staining→ divided into

  1. Chromophobes (C)

     • smallest in size

     • poorely stained

     • contain few cytoplasmic granules

  2. Chromophils (A,B)

     • numerous cytoplasmic granules

     • subdivided into

       • basophils (light blue) BASIC

       • Acidophils (red) ACIDIC

Immunochemical methods and EM of Anterior

Found 5 types of secretory cells

1. somatotrophs→ 50%→ growth hormones

2. corticotrophs→ 20%→ ACTH

3. gonadotrophs→ 5%→ LH and FSH

4. lactotrophs→ 20%→ prolactin

5. thyrotrophs→ 5%→ thyrotrophin

image shows:

• somatotroph filled with secretory granules (S) of moderate size

  • also with mitochondria m, ED and Golgi G

• Size and electron density of granules varies among the different cell types and the hormones they secrete

Major parts of anterior pituitary

1. par distalis (anterior lobe)→ major parts

   1. separated from posterior by pars intermedia

2. Pars tuberalis→ upward extension of anterior pituitary, forms a partial or total collar of cells around the infundibular stem (neural component)

   • together make the pituitary stalk

3. pars intermedia (intermediate lobe)→ thin area of tissue lying against posterior pituitary

   • rudimentary in humans compared to other mammals

   • secretes mealocyte-stimulating hormones (MSH)

Posterior structure

• non-meylinated axons

  • cell bodies are in hypothalamus, supraoptic and paraventricular nuceli

    • where ADH (supraoptic) and oxytocin (paraventricular) are made

• supported by pituicytes→ type of glial cell

  • most nuclei in this are from these

• Highly vascularised

  • fenestrated capillaries (not clearly shown here)

EM of posterior pituitary

Shows

• Pituicytes (P)→ some organelles in cytoplasm but FEW secretory granules

• Non-myelinated axon terminals→ many secretory granules

  • ADH and oxytocin synthezied as precursoler molecules packed in granules and transported down to axons

    • cleavage of percursor into free hormones occurs during transport

Pit and hypothalamus of cat: anatomical features

1. Nuclei - brilliant red

2. Collagen and reticulin – blue

3. Basophilic cytoplasm – blue/purple

4. Acidophilic cytoplasm – orange/red

Identify:

• hypo

• pit

• optic chiasm→ mass of nerve fibres at the anterior limit of hypothalamus

Par distalis (anterior lobe or anterior pit)

• deeply staining area

  • dark red, pale pink and purple cytoplasm

• these are secretory cell in anterior pit, stained different colours due to different hormones

  • GH and PRL→ peptides→ acidophilic

  • ACTH, FSH, TSH and LH→ glycoproteins→ basophilic

  • Depleted hormone contect→ chromophobes→ PALE PINK

Posterior appearance here

• pale staining tissue

• many sections surrounds a fluid filled lumen

  • created as the pituitary stalk grows down from the neural tube

    • during embryonic development