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VAP III > Endocrine 2: diencephalon > Flashcards

Endocrine 2: diencephalon Flashcards

1
Q

What are the components of the diencephalon?

A
  • epithalamus
    • pineal gland (epiphysis cerebri)
  • thalamus “switching centre”
    • subthalamus
    • metathalamus
  • hypothalamus
    • pituitary gland (hypophysis)
    • infundibulum
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2
Q

Where is the diencephalon located?

A

Near the midline of the brain above the mesencephalon (midbrain) and brainstem

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3
Q

Where is the pineal gland on this diagram?

A
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4
Q

Label these structures

A
  1. Hypothalamus
  2. Pituitary
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5
Q

What is the role of the hypothalamus in the endocrine system and where is it located?

A
  • Links the nervous system to the endocrine system
  • Forms part of the walls and floor of the third ventricle and extends rostrally to the optic chiasm
  • Hypothalamo-hypophyseal axis (hypothalamus & pituitary)
    • major control centre for the autonomic nervous system and endocrine system
    • important role in homeostatic regulation of almost all organ systems
    • hypothalamus acts both directly and via pituitary
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6
Q

Where is the hypothalamus on this diagram?

A
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7
Q

Where is the thalamus on this diagram?

A
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8
Q

What is the other name for the pituitary gland?

A

hypophysis

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9
Q

Where is the pituitary gland (hypophysis) on this diagram?

A
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10
Q

Where is the infundibulum on this diagram?

A
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11
Q

What is the name of the saddle-shaped depression in which the pituitary gland (hypophysis) sits in situ?

A

Sella turcica

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12
Q

What bone contains the sella turcica, the saddle-shaped depression that contains and protects the pituitary gland (hypophysis)?

A

Sphenoid bone

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13
Q

What is the term for the “seat” of the sella turcica, the saddle-shaped depression in the sphenoid bone that contains the pituitary gland (hypophysis)?

A

Hypophyseal fossa

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14
Q

What are the two main endocrine functions of the pituiraty gland?

A
  1. secretion of hormones
  2. control of secretion of hormones by endocrine glands/cells
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15
Q

What is the other term for the anterior pituitary? Is it neural or non-neural endocrine tissue?

A

adenohypophysis; non-neural endocrine tissue

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16
Q

What are the three components of the anterior pituitary gland (adenohypophysis)?

A
  1. Pars tuberalis
  2. Pars intermedia
  3. Pars distalis

Exact position and sizes of parts varies amongst species; not all parts present in some groups (e.g. pars intermedia)

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17
Q

What is the other terms for the posterior pituitary gland?

A

neurohypophysis

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18
Q

What are the three components of the posterior pituitary gland (neurohypophysis)?

A
  1. Median eminence (actually part of the floor of the hypothalamus)
  2. Infundibular stalk (interconnecting part)
  3. Pars nervosa (“nervous part” - downgrowth of brain)
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19
Q

The neurohypophysis (posterior pituitary) illustrates the ______ control of _______ cells

A

The neurohypophysis (posterior pituitary) illustrates the neural control of neurosecretory cells

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20
Q

What are the names and functions of the two peptide hormones that are released into the blood in the pars nervosa of the neurohypophysis (posterior pituitary)?

A
  1. Antidiuretic hormone (ADH)
    • Also called vasopressin
    • Water reabsorption in renal collecting gucts and constriction of arterioles
    • Social bonding roles (?)
  2. Oxytocin
    • Contration of the uterus during birth
    • Ejection of milk by mammary glands during suckering
    • Social/maternal bonding
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21
Q

ADH and oxytocin are synthesised by neurosecretory cells with large cell bodies in which two nucleui within the hypothalamus?

A
  1. Paraventricular nucleus
  2. Supraoptic nucleus
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22
Q

Axons of neurosecretory cells that have their cells bodies in the paraventricular and supraoptic nuclei of the hypothalamus extend in tracts along the _______ stalk to the _______ ______ of the __________. Secretory vessels are transported down the axon to the axon ________. Hormones ADH and oxytocin are released by __________ when cells generate action potentials.

A

Axons of neurosecretory cells that have their cells bodies in the paraventricular and supraoptic nuclei of the hypothalamus extend in tracts along the infundibular stalk to the pars nervosa of the neurohypophysis (posterior pituitary). Secretory vessels are transported down the axon to the axon terminal. Hormones ADH and oxytocin are released by exocytosis when cells generate action potentials.

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23
Q

Neurosecretory cells in the PVN (paraventricular nucleus) and SON (supraoptic nucleus) receicve and integrate synaptic input from a host of typical neurons, for example vasopressin cells.

What information do vasopressin cells track and what are the outcomes in terms of ADH production and its effects?

A
  • Vasopressin cells receive input about blood volume and plasma osmotic concentration
  • Low blood volume and/or high plasma osmolarity leads to ADH secretion and conservation of water
24
Q

What is Diabetes insipidus (DI)? What are its two defining characters and two types of causes?

A
  • Disorder of water metabolism
  • Characterised by
    1. Polyuria (large volume of dilute urine + incontinence)
    2. Polydipsia (excessive drinking of water)
  • Caused by
    1. Defective secretion of ADH (central DI), or
    2. Inability of renal collecting ducts to respond to ADH (nephrogenic DI)
25
Q

What are some characteristics of central diabetes insipidus (DI)?

A
  • lack/low levels of circulating ADH
  • Can be primary (idiopathic and congenital) or secondary (head trauma, neoplasia, drug-induced)
  • May appear at any age, in any breed of dog or cat
  • Mostly appears in young animals (~6 mths)
  • There is no hyperglycaemia as in diabetes mellitus, so no glycosuria
26
Q

What is SIADH?

A
  • Syndrome of inappropriate ADH secretion
  • Hypersecretion of ADH (opposite of DI) in the absence of osmotic or volumetric signals
  • Cause is usually neoplastic (i.e. tumour)
27
Q

What are the structures labelled P and H in this neurohypophyseal histological section?

A

H = herring bodies: distended axon terminals where secretory granules containing hormones collect

P = Pituicytes: specialised glial cells that support neurosecretory functions (cannot distinguish from other cell types easily in H&E stain)

28
Q

The adenohypophysis (anterior pituitary) illustrates _______ control of ______ cells.

A

The adenohypophysis (anterior pituitary) illustrates neurosecretory control of endocrine cells.

29
Q

What is the name of the neurosecretory cells in the hypothalamus that control secretions of the anterior pituitary gland (adenohypophysis)?

A

Parvocellular neurons

30
Q

Neurosecretory cells (parvocellular neurons) in the hypothalamus secrete _____ and ______ neurohormones at the capillaries of the ________ eminence to control hormone production by endocrine cells in the adenohypophysis (anterior pituitary).

A

Neurosecretory cells in the hypothalamus secrete releasing and inhibiting neurohormones at the capillaries of the median eminence to control hormone production by endocrine cells in the adenohypophysis (anterior pituitary).

31
Q

What is the name of the portal vessels that transport releasing and inhibitory neurohormones from capillaries at the median eminence (hypothalamus) to capillaries in the adenohypophysis (anterior pituitary)?

A

Hypothalamo-hypophysial portal vessels

32
Q

What are the two main groups of anterior pituitary (adenhohypophysis) hormones, grouped according to their target tissues? Examples of each?

A
  1. Direct acting hormones:: exert principal effects on nonendocrine tissues
    • Growth hormone (GH; somatotropin)
    • Prolactin (PRL)
    • Melanocyte-stimulating hormone (MSH - some animals only)
  2. Tropic hormones: control other endocrine tissues
    • Thyroid-stimulating hormone (TSH; thyrotropin)
    • Adrenocorticotropic hormone (ACTH; corticotropin)
    • Follicle-stimulating hormone (FSH)
    • Luteinising hormone (LH)
33
Q

What are some of the functions of growth hormone (GH; somatotropin)? Is this a tropic or a non-tropic hormone?

A
  • Produced by the adenohypophysis
  • GH stimulates many cells in the body to produce growth factors such as IGF-1 (insulin-like growth factor-1)
    • These growth factors have a paracrine function
  • GH also has direct affects on growth and nutrient metabolism in many tissues, especially bone and muscle
  • This means that it plays both tropic and non-tropic roles
34
Q

What is the name of the type of growth hormone (GH)-producing tumour that can result in gigantism or acromegaly?

A

pituitary adenoma

35
Q

What is gigantism and what causes it?

A
  • Abnormally high linear/height growth
  • Cause usually a GH-producing tumour called pituitary adenoma
    • → excess GH → excess IGF-1 before epiphyseal plates close (in young)
36
Q

What is acromegaly and what causes it?

A
  • Clinical signs:
    • Enlargement of limbs, facial teatures, organs, and excessive growth in other organs or tissues
    • insulin-resistant diabetes mellitus
    • respiratory/heart disease (depends upon affected tissues)
    • Particularly common in cats
    • Rare in dogs
  • Cause usually a GH-producing tumour called pituitary adenoma
    • → excess GH → excess IGF-1 after epiphyseal plates close (adulthood)
  • In dogs may be caused by exess progesterone leading mammary glands to secrete excess GH
37
Q

What are the pituitary gonadotropins produced by the adenohypophysis, and what are their actions in traget cells?

A
  • Tropic hormones produced by the adenohypophysis that stimulate the production of sex hormones in the gonads and regulate the growth and maturation of germ cells
  • Follicle-stimulating hormone (FSH) - sperm production (males) and follicle development and secretion (females)
    • Testes → inhibin
    • Ovaries → Estradiol
  • Luteinizing hormone (LH)
    • Testes → testosterone
    • Ovaries → progesterone
38
Q

What is ACTH and what are its main target tissues and actions?

A
  • Adrenocorticotropic hormone (also called corticotropin) is a tropic hormone produced by the adenohypophysis
  • Targets the adrenal cortex to stimulate production of steroid hormones such as cortisol and corticosterone
39
Q

What is TSH and what are its main target tissues and actions?

A
  • Thyroid-stimulating hormone (also called thyrotropin) is a tropic hormone
  • Targets the thyroid gland
    • Stimulates growth of thyroid gland
    • Stimulates production of thyroid hormones (e.g. thyroxine, triiodothyronine)
40
Q

What is prolactin and what are its main target tissues and actions?

A
  • Prolactin is a non-tropic hormone produced by the adenohypophysis
  • Targets mammary glands
    • growth, development, differentiation, milk production
  • In some species it also supports the function of the corpus luteum (a temporary endocrine structure in ovaries that is involved in the production of relatively high levels of progesterone and moderate levels of estradiol and inhibin A)
  • In various non-mammal vertebrates it supports a variety of functions like:
    • reproduciton, water and ion balance, caring for young
41
Q

What are the cells labelled A and B in this histological image of the adenohypophysis?

A
  • Chromophils
    • A = acidophils, B = basophils
    • Secretory function evidenced by strong staining
42
Q

What are the cells labelled Cp in this histological image of the adenohypophysis?

A
  • Chromophobes
    • Few secretory granules, evidenced by weak staining
43
Q

The adenohypophysis is composed of clumps and cords of [______] cells, separated by large
diameter fenestrated [______].

A

The adenohypophysis is composed of clumps and cords of epitheloid cells, separated by large
diameter fenestrated capillaries.

44
Q

What are the five hormone-producing cell types in the adenohypophysis, what is their distribution as a percentage, and what hormone does each produce?

A
  1. Somatotrophs (S) (50%)
    • GH
  2. Corticotrophs (C) (20%)
    • ACTH
  3. Thyrotrophs (T) (5%)
    • TSH
  4. Gonadotrophs (G) (5%)
    • FSH, LH
  5. Mammotrophs (20%)
    • Prolactin
45
Q

How is adehohypophysis (anterior pituitary) hormone secretion regulated?

A
  • Negative feedback
    • Short loop feedback: High levels of anterior pituitary tropic hormones increase
      target gland hormone secretion but decrease releasing hormone secretion by the hypothalamus
    • Long loop feedback: High levels of target organ hormones decrease secretion
      by both the hypothalamus & anterior pituitary
46
Q

What is pulsatile secretion and how is it helpful?

A
  • Secretion of many hypothalamic & pituitary hormones is pulsatile
  • Results in intermittent periods of high [hormone] in blood
  • pulsatile secretion helps prevent desensitisation
    • If a hormone is continuously present at high levels, target cells may down-regulate receptors for that hormone
  • Synaptic input to neurosecretory cells governs pulsatile release of hypothalamic
    hormones → this causes pulsatile output of pituitary hormones
    • e.g. CRH (Corticotrophin-releasing hormone) neurons secrete pulses 2-3x per hour, amplitude can vary by time of day (input from circadian clock) & increases during stress
      • Hypothalamus (CRH, also called ACTHRH) → Adenohypophysis (Adenohypophysis (ACTH, also called corticotropin) → Adrenal cortex (glucocorticoids = stress hormones)
47
Q
A
48
Q

What are three examples of axes that comprise a hormonal relationship between the hypothalamus, pituitary, and a more remote endocrine gland?

A
  1. Hypothalamo-pituitary-thyroid (HPT) axis
    • thyrotropin releasing hormone (TRH), thyroid stimulating hormone (TSH)
  2. Hypothalamo-pituitary-gonadal (HPG) axis
    • gonadotropin-releasing hormone (GnRH), LH, FSH
  3. Hypothalamo-pituitary-adrenal (HPA) axis
    • Corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH)
49
Q

What does GnRH stand for, where is it produced, and what does it affect?

A
  • Gonadotropin-releasing hormone
  • a tropic peptide hormone synthesized and released from GnRH neurons within the hypothalamus
  • responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the adenohypophysis (anterior pituitary)
50
Q

What does TRH stand for, where is it produced, and what does it affect?

A
  • Thyrotropin-releasing hormone
  • produced by neurons in the hypothalamus
  • stimulates the release of thyroid-stimulating hormone (TSH) and prolactin from the anterior pituitary (adenohypophysis)
51
Q

What does CRH stand for, where is it produced, and what does it affect?

A
  • Corticotropin-releasing hormone
  • also known as corticotropin-releasing factor (CRF) or corticoliberin
  • CRH is secreted by the paraventricular nucleus (PVN) of the hypothalamus in response to stress
    • CRH is also synthesized in peripheral tissues, such as T lymphocytes, and is highly expressed in the placenta
  • Its main function is the stimulation of the anterior pituitary (adenohypophyseal) synthesis of ACTH (adrenocorticotropic hormone) - the principal effects of which are increased production and release of cortisol by the cortex of the adrenal gland
52
Q

What is another name for the pineal gland? Where is it located?

A
  • epiphysis
  • Roof of the 3 rd ventricle of the brain dorsally evaginates out of the midbrain
53
Q

What is the role of the epiphysis and how does it achieve this?

A
  • Adjusts endogenous physiological rhythms such as sleep, hormone levels,
    and appetite to diurnal and seasonal cycles
  • Secretes melatonin from pinealocytes into blood & CSF based on light dark cycles → special sensory ganglion cells in retina
  • Light inhibits enzymes involved in melatonin production = secreted at night
54
Q

What are the cells labelled (P) in this pineal (epiphysis) histological image? What is their function?

A
  • Pinealocytes: pineal chief cells
    • Modified neurons arranged in clusteres surrounded by fenestrated capillaries
    • Secrete melatonin
55
Q

What are the cells labelled (N) in this pineal (epiphysis) histological image? What is their function?

A
  • Neuroglia
    • support cells
56
Q

What are the structures labelled (S) in this pineal (epiphysis) histological image?

A
  • Ageing pineal glands may contain mineral plaques “pineal sand”
    • extracellular bodies consisting of concentric layers of calcium and magnesium phosphate

VAP III (11 decks)

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