L1 endocrine anatomy Flashcards
endocrine glands general structure?
Are ductless and secrete hormones
Endocrine response is slower than neuro response because:
Hormones are released from specific cells
Hormones have to diffuse to & cross capillary wall; blood transport is slower than nerves
Relies on diffusion once hormone leaves the vascular system
Some chemicals serve as both neurotransmitters and hormones ?
E.g. Adrenaline (epinephrine) and noradrenaline (norepinephrine)
Both of these molecules are produced by the adrenal glands as well as being a neurotransmitter and are part of the sympathetic response (fight or flight)
‘Local’ Hormones
Have a local effect, i.e. only travel a short distance to effector tissue
Usually only small amounts are found in the general circulation
e.g. secretin and cholecystokinin
Includes paracrine hormones which don’t enter vasculature to reach their target organ
e.g. gastrin and epidermal growth factor
‘General’ hormones
Secreted by specific endocrine glands
Transported around the body in blood
Cause many different reactions
e.g. adrenaline (epinephrine) and noradrenaline (norepinephrine) secreted from adrenal medulla
Some hormones have general and local effects
e.g. testosterone secreted from Leydig cells
Some hormones have very set target tissues with specific receptors
e.g. ACTH from anterior pituitary causes release of adrenocortical hormones from the adrenal cortex
List 4 types of hormones based on chemistry
- Steroid hormones
- Protein hormones
- Tyrosine hormones
- Fatty acid hormones(eicosanoids)
Carrier molecules
Hormones may circulate freely or be bound to carrier molecules
Free hormones degrade quickly while bound ones last longer
Carrier molecules usually proteins
Steroid hormones
hormones that structure related to cholesterol
Cells vacuolated, lots lipid, mitochondria, SER
Cortisol, aldosterone, oestrogen, progesterone, testosterone
Protein hormones
Proteins, polypeptides, amino acid hormones
Cells dense staining with secretory granules
Lots mitochondria, RER, ribosomes
ADH, oxytocin, insulin, glucagon, parathyroid h.
Tyrosine hormones
Catecholamines ( hormones made by adrenal glands), thyroid hormones
Endocrine organs are classically characteristised by >
an endocrine organ contains tissue which releases hormone directly into the blood
Fatty acid hormones (eicosanoids)
Derived from arachadonic acid
Prostaglandins, prostacyclins, leukotrienes & thromboxanes
List the organs that are primarily endocrine
Pituitary, pineal, thyroid, parathyroid, adrenals
List the organs that combine endocrine Fx with other major functions
Testes, ovary, pancreas, placenta
endocrine organs which have relatively incidental endocrine Fx (diffuse endocrine system)
- Kidney, Liver, thymus, heart, GI tract
- Often paracrine rather than endocrine
Three types of endocrine organs
Three types
Organs that are primarily endocrine
Combines endocrine function with other major functions
Relatively incidental endocrine function (‘diffuse endocrine system’)
Typical Endocrine Gland Characteristics
Scattered throughout body and a range of embryological origins
Secrete hormones from cells that are usually derived from epithelial cell origins
Ductless
Highly vascular
Sparse connective tissue framework
Different Morphology of endocrine glands (4)
- Follicular
- Cell masses or cords
- Solitary endocrine cells
- Neurocrine cells
Morphology of endocrine gland Follicular
Thyroid, ovary
- -> Hormones stored in follicle lumen but reabsorbed to enter capillary network
- -> follicular in nature but no ducts
Morphology of endocrine glands Cell masses or cords
Pituitary, adrenal cortex, interstitial tissue of testis, JG cells
Morphology of endocrine gland solitary endocrine cells
Enteroendocrine cells
Morphology of endocrine glands –> neurocrine cells
Typical neurone cells whose products are released into the blood
hypothalamus, pineal
Fx of hormones (4)
Reproduction (sex hormones)
Growth and development (TH and GH)
Maintenance of internal environment (adrenals, parathyroid)
Energy production and storage (thyroid and pancreatic hormones)
Essential for life – deficiencies or excess can occur
Hyperadrenocorticism
Cushings disease
List all the areas where endocrine tissue is found
Parathyroid Thyroid pineal hypothalamus pituitary thymus stomach intestine testis placenta uterus ovary kidney adrenal
Endocrine organs of the head region
Hypothalamus
At base diencephalon on floor of 3rd ventricle
Immediately above the pituitary gland
‘Master gland’ as it controls the release of many of other hormones from pituitary
Integrates endocrine & CNS
Neurosecretory neurons extend down into pituitary
Hormones are all small polypeptides
2 routes of horse release by the hypothalamus
- Neurosecretory cells
2. Hormones released
Neurosecretory cells pathway of the hypothalamus
manufacture and transport their hormones via their axons to the posterior pituitary (neurohypophysis) in neurosecretory granules
Hormones stored in disteneded ends of axons (Herring bodies) until secretion
2 hormones released:
antidiuretic hormone (ADH or vasopressin; SO nuc.)
Oxytocin (PV nuc.)
Other neurosecretory cells in the hypothalamus
Other neurosecretory cells in the hypothalamus
release hormones into the hypothalamic-pituitary portal vessels that travel to the anterior pituitary (adenohypophysis)
cause release or inhibition of the trophic hormones of the anterior pituitary
Hypothalamic hormones that use the hypothalamus-pituitary portal system include:
Corticotrophin releasing hormone/factor (CRH/F)
Growth hormone release-inhibiting hormone (GHRIH/ somatostatin/ somatotrophin release inhibiting factor)
Prolactin release-inhibiting hormone (PRIH or dopamine)
Thyroid releasing hormone (TRH)
Gonadotropin releasing hormone/ factor (GnRH)
B. Pituitary (Hypophysis) –? Consists of 2 regions of different tissue type
Anterior pituitary (adeno-hypohysis) composed of: Pars distalis (P. anterior) Pars intermedia Pars tuberalis
Posterior pituitary (neuro-hypophysis) composed of:
Pars nervosa (P. posterior)
Infundibulum
Median eminence
Embryology of the pituitary
Diaphragm sellae =
horizontal fold of dura, forms roof of sella turcica
Median eminence
Infundibulum
Sella turcica
Median eminence = stalk with 3rd ventricle
Infundibulum
= pituitary stalk
Sella turcica
= small depression in basisphenoid
Hormones of the pituitary
Anterior pituitary Adrenocorticotrophic h. (ACTH) Thyroid stimulating h. (TSH) Gonadotrophic hh. Follicle stimulating h. (FSH) Luteinising h. (LH) Growth h./ somatotrophic h. (GH/ STH) Prolactin α-melanocyte stimulating h. (MSH; from pars intermedia)
Posterior pituitary
Oxytocin
Antidiuretic h. (ADH)/ vasopressin
Histology of the pituitary gland
Histo - andenohypophysis
Cords of cells & sinusoidal capillaries
Cells classed dye affinity Chromophils (A & B) Active, lots secretory granules Somatotrophs 45% Mammotrophs 20% Corticotrophs 20% Thyrotrophs 5% Gonadotrophs 5%
Chromophobes (C)
Resting?
Hsiotology of the hypophysis (cont) –> pars Intermedia (of adenohypophysis)
Histology of hypophysis Neurophyopophysis
Cone of Wulzen
=outpocket of pars intermedia that looks more like adenohypophysis in OX
Pineal Gland = Epiphysis
Small, darkly pigmented outgrowth from dorsum 3rd ventricle
Sits between cerebral hemispheres & cerebellum
Foci of calcification ‘brain sand’ in advanced age
Main hormone is melatonin
Functions of the Pineal gland
Regulates diurnal and circadian rhythms
Light → retina → hypothalamus → sympathetic fibres → pineal
↑ daylight → ↓ melatonin
Melatonin secreted into blood or CSF of 3rd ventricle
Alters secretion of gonadotrophic hormones by anterior pituitary
Long day breeders e.g. horse ↑ daylight → ↓ melatonin → ↑ ovarian function
Short day breeders e.g. goat ↓ daylight → ↑melatonin → ↑ ovarian function
Other functions of the pineal gland
- Inhibits puberty
Antigonadotophic effects
Relatively active prepubescent animals - Regulates daily fluctuations of corticosteroids
Circadian clock in suprachiasmic nucleus - Photoreceptor in lower vertebrate
Regulates colour change
Histology of pineal gland
S – brain sand
P – pinealocytes (pineal chief cells)
N – neuroglial cells
