IV. ENDOCRINE SYSTEM
For each one of the glands with internal secretion, knowledge is required about the development,
microscopicstructure, cytophysiology, blood supply and innervation.
83. Pituitary gland.
84. Epiphysis.
85. Thyroid gland, parathyroid glands.
86. Suprarenal gland. Paraganglia.
87. Endocrine pancreas. Gastro-entero-pancreatic system.
83. PITUITARY GLAND
- Endocrine system produces hormones that regulate activities of various cells, tissues + organs in the
body.
- Hormones coordinate body growth + development
- Hormones have 2 controls:
Paracrine control:
- Hormones released act on adjacent cells + targeted cells through receptors
Autocrine control:
- Some cells express receptors for hormones they secrete + regulate their own activity
3 types of hormones are produced:
1. Steroid
a. Cholesterol derived compounds
b. Synthesised + secreted by cells of ovaries, testes + adrenal cortex
c. E.g. gonadal + adrenal cortical steroids released into blood stream + carried by special
carrier proteins such as androgen binding proteins
2. Small peptides, polypeptides + proteins:
a. These hormones readily dissolved in blood
b. Synthesised + released by cells of hypothalamus, pituitary gland, thyroid gland, parathyroid
gland, pancreas
c. E.g. insulin, glucagon, growth hormone, FSH, LH, ADH, oxytocin, interleukins
3. Amino acids + derivaties
a. Including catecholamines (norepinephrine + epinephrine) + prostaglandins, prostacyclins +
leukotrienes
b. Synthesised + secreted by many neurons + adrenal medulla
c. Thyroid hormones released by thyroid gland
d. Catecholamines dissolve in blood but thyroid hormones do not so require pre-albumin
(thyroxin binding protein)
- Hormones binds to the receptors on the target cells + mediate response.
o There are 2 types of hormone receptors
1. Cell surface receptors
a. For peptide hormones or catecholamines that cant penetrate cell membrane
b. Activate G-protein
c. Second messengers required
2. Intracellular receptors
a. Localised within the cell (within nucleus)
b. For steroids + thyroid hormones that penetrate cell membrane
c. These receptors have 3 domains:
i. Hormone binding region
ii. DNA binding region
1
, iii. Amino-terminal region
d. Hormone binds receptor – RNA polymerase activity – mRNA – new protein
Pituitary gland:
- Pea sized gland weighs 0.5g in male + 1.5g multiparous woman
- Located at the base of brain lies in depression of sphenoid bone called bella turcica
- Infundibulum: vascular network connecting the pituitary gland to hypothalamus
o 2 functional components
1. Adenohypophysis (anterior lobe)
a. Glandular epithelial tissue
b. Evagination of ectoderm of oropharynx (rathke’s pouch) during embyogenesis
i. Consist of:
1. Pars distalis
2. Pars intermedia
3. Pars tuberalis
2. Posterior lobe (neurohypophysis)
a. Neural tissue
b. Derives from neuroectoderm of 3rd ventricle of developing brain
i. Consist of:
1. Pars nervosa
2. Has neurosecreting axons infundibulum
3. Forms hypothalamohypophysial
Anterior lobe:
- Cells here are organised in clumps + cords, separated by fenestrated sinusoidal capillaries
- Clumps + cords respond to signals from hypothalamus + synthesise pituitary hormones
- Hormones by A.pituitary gland are:-
o ACTH, TSH, FSH, LH = tropic hormones
▪ Because these hormones regulate activity of cells in other endocrine glands
o GH, PRL = these hormones act directly on target organs
- 3 types of cells according to their staining properties
o Basophils vesicle cells: produce TSH, ACTH, FSH + LH
o Acidophils vesicle cells: GH (somatotrophin) + prolactin
o Chromophobes
o Lactotropes (prolactin)
▪ 15 – 20% of parenchymal cells in A.lobe
▪ Large cells polygonal with oval nuclei
o Corticotropes (ACTH cells)
▪ 15 – 20% of parenchymal cells in A.lobe
▪ Polygonal cells with eccentric nuclei producing proopiomelanocortin (POMC)
• Precursor to ACTH
o Gonadotropes (FSH + LH cells)
▪ 10% of parenchymal cells in A.lobe
▪ Small, oval cells with eccentric nuclei
o Thyrotropes (TSH cells)
▪ 5% of parenchymal cells in A.lobe
▪ Round + eccentric nuclei
▪ TSH also stimulate productions of PRL
▪ TSH also acts on follicular cells of thyroid gland
• Thyroid hormones produced
- All these cells are with pars details
2
For each one of the glands with internal secretion, knowledge is required about the development,
microscopicstructure, cytophysiology, blood supply and innervation.
83. Pituitary gland.
84. Epiphysis.
85. Thyroid gland, parathyroid glands.
86. Suprarenal gland. Paraganglia.
87. Endocrine pancreas. Gastro-entero-pancreatic system.
83. PITUITARY GLAND
- Endocrine system produces hormones that regulate activities of various cells, tissues + organs in the
body.
- Hormones coordinate body growth + development
- Hormones have 2 controls:
Paracrine control:
- Hormones released act on adjacent cells + targeted cells through receptors
Autocrine control:
- Some cells express receptors for hormones they secrete + regulate their own activity
3 types of hormones are produced:
1. Steroid
a. Cholesterol derived compounds
b. Synthesised + secreted by cells of ovaries, testes + adrenal cortex
c. E.g. gonadal + adrenal cortical steroids released into blood stream + carried by special
carrier proteins such as androgen binding proteins
2. Small peptides, polypeptides + proteins:
a. These hormones readily dissolved in blood
b. Synthesised + released by cells of hypothalamus, pituitary gland, thyroid gland, parathyroid
gland, pancreas
c. E.g. insulin, glucagon, growth hormone, FSH, LH, ADH, oxytocin, interleukins
3. Amino acids + derivaties
a. Including catecholamines (norepinephrine + epinephrine) + prostaglandins, prostacyclins +
leukotrienes
b. Synthesised + secreted by many neurons + adrenal medulla
c. Thyroid hormones released by thyroid gland
d. Catecholamines dissolve in blood but thyroid hormones do not so require pre-albumin
(thyroxin binding protein)
- Hormones binds to the receptors on the target cells + mediate response.
o There are 2 types of hormone receptors
1. Cell surface receptors
a. For peptide hormones or catecholamines that cant penetrate cell membrane
b. Activate G-protein
c. Second messengers required
2. Intracellular receptors
a. Localised within the cell (within nucleus)
b. For steroids + thyroid hormones that penetrate cell membrane
c. These receptors have 3 domains:
i. Hormone binding region
ii. DNA binding region
1
, iii. Amino-terminal region
d. Hormone binds receptor – RNA polymerase activity – mRNA – new protein
Pituitary gland:
- Pea sized gland weighs 0.5g in male + 1.5g multiparous woman
- Located at the base of brain lies in depression of sphenoid bone called bella turcica
- Infundibulum: vascular network connecting the pituitary gland to hypothalamus
o 2 functional components
1. Adenohypophysis (anterior lobe)
a. Glandular epithelial tissue
b. Evagination of ectoderm of oropharynx (rathke’s pouch) during embyogenesis
i. Consist of:
1. Pars distalis
2. Pars intermedia
3. Pars tuberalis
2. Posterior lobe (neurohypophysis)
a. Neural tissue
b. Derives from neuroectoderm of 3rd ventricle of developing brain
i. Consist of:
1. Pars nervosa
2. Has neurosecreting axons infundibulum
3. Forms hypothalamohypophysial
Anterior lobe:
- Cells here are organised in clumps + cords, separated by fenestrated sinusoidal capillaries
- Clumps + cords respond to signals from hypothalamus + synthesise pituitary hormones
- Hormones by A.pituitary gland are:-
o ACTH, TSH, FSH, LH = tropic hormones
▪ Because these hormones regulate activity of cells in other endocrine glands
o GH, PRL = these hormones act directly on target organs
- 3 types of cells according to their staining properties
o Basophils vesicle cells: produce TSH, ACTH, FSH + LH
o Acidophils vesicle cells: GH (somatotrophin) + prolactin
o Chromophobes
o Lactotropes (prolactin)
▪ 15 – 20% of parenchymal cells in A.lobe
▪ Large cells polygonal with oval nuclei
o Corticotropes (ACTH cells)
▪ 15 – 20% of parenchymal cells in A.lobe
▪ Polygonal cells with eccentric nuclei producing proopiomelanocortin (POMC)
• Precursor to ACTH
o Gonadotropes (FSH + LH cells)
▪ 10% of parenchymal cells in A.lobe
▪ Small, oval cells with eccentric nuclei
o Thyrotropes (TSH cells)
▪ 5% of parenchymal cells in A.lobe
▪ Round + eccentric nuclei
▪ TSH also stimulate productions of PRL
▪ TSH also acts on follicular cells of thyroid gland
• Thyroid hormones produced
- All these cells are with pars details
2
