quiz 2 Flashcards
1
Q
anatomy and characteristics of the hypothalamus
A
- part of the diencephalon
- primary relay and processing center for sensory information and autonomic control
Characteristics:
- lies inferior to the thalamus
- contributes to the wall of the 3rd ventricle
2
Q
functional connections between posterior pituitary and hypothalamus
A
1) posterior is an outgrowth of the brain and maintains its neural connections
* neurons in the supraoptic (SON) and paraventricular nuclei (PVN) of the hypothalamus give rise to the hypothalamic-hypophyseal tract
2) oxytocin is predominantly synthesized by PVN
3) Antidiuretic hormone is predominantly synthesized by SON
3
Q
functional connections between anterior pituitary and hypothalamus
A
1) anterior lobe is derived from epithelial tissue
2) no direct connection between anterior pituitary and hypothalamus
* connection is vascular:
- hypophyseal portal system
- connects Medien eminence to secretory cells of the anterior pituitary
3) releasing and inhibiting hormones secreted by hypothalamus are carried by portal system to anterior pituitary
* these hypophysiotropic factors regulate the activity of secretory cells in anterior pituitary
4
Q
magnocellular system
A
- supraoptic nuclei (SON) : synthesize vasopressin (ADH)
- paraventricular nuclei (PVN) ; synthesize oxytocin
5
Q
parvocellular neurosecretory system
A
- ventral hypothalamic nuclei
- axons of these neurons converge toward the pituitary stalk (about the primary plexus of the portal system of the median eminence
- synthesize and secrete hypophysiotropic factors
6
Q
hypophyseal portal system
A
anterior pit and hypo
1) primary plexus: drains interstitial space of the median eminence
2) hypophyseal portal veins
3) secondary plexus: delivers hypophysiotropic factors of the hypothalamus to the adenohypophysis
7
Q
TRH - thyrotropin releasing hormone
A
- hypophysiotropic hormone
- controls TSH secretion which is released from anterior pituitary
8
Q
SST (somatostatin)
A
- inhibits GH secretion from anterior pituitary
* acts on pituitary somatrophs
9
Q
GHRH - growth hormone releasing hormone
A
- stimulates GH secretion from anterior pituitary
- invovled with ghrelin
10
Q
Ghrelin
A
Activates GHRH receptors and GH release
- Ghrelin is a 22 aa peptide made by stomach, small intestine, and hypothalamus
- it regulates brain circuits involved in feeding behavior and energy homeostasis
11
Q
GnRH - gonadtropin releasing hormone
A
- stimulates the release of FSH and LH from anterior pituitary
- primary brain based control of gonadtropins
functional considerations -pulsate release -frequency determines which hormone is released low frequency= FSH release high frequency = LH release
12
Q
CRH - corticotropin releasing hormone
A
-stimualtes the release of ACTH from anterior pituitary
- crh neurons co express vassopressing AVP
- released in response to stress
13
Q
PIF - prolactin release inhibiting factor (DA)
A
- inhibits the secretion of PRL from the hypothalamus
- PIF is a dopamine
14
Q
Control of hypothalamic hormone secretion - general mechanisms
A
- Hypothalamus is controlled by other brain circuits
- **These brain circuits are activated by circuits processing extrinsic and intrinsic cues
- **Extra-hypothalamic neurons innervate hypophysiotropic hormone producing cells
- Brain-based activity requires synaptic transmission
- **Specific neurotransmitters (NT’s) released by circuits terminating in hypothalamus control hormone secretion
- **NT’s are typically monoamines i.e. nor-epinephrine (NE); dopamine (DA); epinephrine (Epi); serotonin (5-HT); Histamine; acetylcholine (Ach)
- Nature of effect is mediated by NT receptors
- **Increase or decrease release of hypothalamic hormones
15
Q
Control of hypothalamic hormone secretion - neurotransmitters regulating hormone secretion of CRH
A
- multiple systems involved in the repsonse to stress
- *ACh - acetycholine
- *Catecholamines (NE, EPI, DA)
- neurons releasing these neurotransmitters have projection to the PVN
- activation of these circuits leads to an increase in CRH secretion
16
Q
Control of hypothalamic hormone secretion - neurotransmitters regulating hormone secretion of PIF
A
- Prolactic (PRL) is released during suckling
- *DA tonically inhibits PRL
- inhibition of DA neurons dis-inhibits PRL secretion
- *increase serotonin leads to an increase in PRL secretion
- *sereotinin inhibits DA releasing neurons
17
Q
Control of hypothalamic hormone secretion - neurotransmitters regulating hormone secretion of GHRH
A
-central serotonin and noradrenalin stimulates the secretion of GHRH
18
Q
Control of hypothalamic hormone secretion - neurotransmitters regulating hormone secretion of GnRH
A
multiple mechanisms
- control of reproduction is highly evolved
- many higher brain systems may affect reproduction
- many other organ systems may affect reproduction
multiple NT’s may affect GnRH release
- NE, GABA, Glutamate, Neuropeptide Y, 5-HT
- DA leads to an increase in GnRH secretion
19
Q
Control of hypothalamic hormone secretion - neurotransmitters regulating hormone secretion of TRH
A
-NE and Epi released in association with sympathetic NS activation lead to an increase in TRH secretion
20
Q
feedback control of the hypothalamus and pituitary
A
look at diagram
ACTH –> adrenal cortex –> cortisol
FSH/LH –> gonads (ovary –> estradiol) (testis–> testosterone )
TSH –> thyroid –> thyroxine
21
Q
long loop negative feedback
A
- three hormone systems
- third hormone can suppress the release of the first or second hormone
- peripheral hormone inhibits both the pituitary and hyppthalamus
22
Q
short loop negative feedback
A
- two hormone systems
- second hormone can suppress the release of the first hormone
- pituitary hormone inhibits hypothalamus
23
Q
autoinhibition
A
-hormone can suppress its own release
24
Q
feedback control of hypothalamic CRH
A
CRH –> ACTH –> glucocorticoid release
cortisol is the predominant glucocorticoid
Glucocorticoids inhibit both the hypothalamus and pituitary
**cortisol decreases CRH and ACTH
CNS–> hypothalamus –CRH–> anterior pit –ACTH–> Adrenal cortex –Cortisol–> target tissues
25
Feedback control of hypothalamic GnRH
GnRh --> FSH and LH --> estrogens and androgens
- steorid hormones predominantly inhibit the hypothalamus
- in females, estrogen also acts on the pituitary
* *Estrogen decreases FSH but increases LH
26
Feedback control of pituitary PRL
PRL inhibits hypothalamic release of PIF (DA)
27
Feedback control of pituitary GH
-GH release and controlled by the combined effects of SST and GHRH
GHRH--> GH --> somatomedin (insulin like growth factors) from liver
- somatomedins increase tissue growth
- IGF increases muscle and skeletal growth
IGF increases SST from hypothalamus
SST decreases GH from pituitary
GH increases SST from hypothalamus
28
Feedback control of hypothalamic TRH
TRH --> TSH --> T3/T4
T3/T4 decreases TSH from pituitary and decreases TRH from hypothalamus
29
Structure of pituitary gland (Hypophysis)
Adenohypophysis - anterior lobe
Neurohypophysis - posterior lobe
30
Anterior lobe forms
(adenohypophysis) forms as an out pouching of the oral ectoderm -Rathke’s pouch
- Rathke’s pouch migrates dorsally and separates from the developing oral cavity
31
Posterior lobe forms
(neurohypophysis) forms from neuroectoderm of the floor of the forebrain
32
what is infundibulum
- part of posterior lobe
- is an out pouching of the floor of the diencephalon
-Neuroepithelial cells proliferate and then differentiate into pituicytes
-Axons grow into the infundibulum from hypothalamic nuclei
33
Anterior lobe has
ACTH, GH, TSH, PRL, LH, FSH
and is responsible for
-metabolism, growth and development, reproduction, lactation (development), response to stress
34
Posterior lobe has
OT, AVP
and is responsible for
water balance and parturition (childbirth) and lactation projection
35
lactotroph cell releases
prolactin (PRL) Acidophil
36
somatotropin cell releases
growth hormone (GH) acidophil
37
thyrotroph cell releases
thyrotropin (TSH) basophil
38
gonadotroph cell releases
LH (lutropin) and FSH (Follitropin) both basophil
39
corticotrophin cell releases
corticotropin (ACTH) basophil
40
what does troph cell mean
cell releasing/producing hormone
41
peptide growth hormones GH and PRL are
Structurally similar peptides
Affect body growth
GH - Generalized effects on body cells
PRL - Selective effect on mammary tissue
42
classification of GH
Anabolic protein hormone
Indirect effects mediated by IGF’s
**growth all over body
Increases amino acid incorporation into muscle
Increases collagen incorporation into extracellular matrix
Direct effects
*glusose sparing effects by targeting adipose tissue, aklso effects skeltal, muscle, bones, adipose
Oppose effects of insulin
Increase blood glucose levels
43
classification of prolactin
Functions
-Mammary gland growth
-Lactogenesis
Elevated during pregnancy and postpartum lactational period
-Estrogen → ↑ PRL release
-Estrogen → ↑ mitosis in lactotrophs
In males PRL affects LH receptor function
-LH → ↑ testosterone production
-Testosterone affects the rate of spermatogenesis
Release of PRL is episodic
-Surges during sleep
44
classification of glycoproteins - LH, FSH, TSH
unique B (beta) subunit)
45
classification of TSH
-Synthesized and secreted by basophilic thyrotrophs in pars distalis of the pituitarygland
-Control thyroid function
** Production and release of T3 and T4
46
classification of LH
- Control production of steroid hormones by the gonads
- Control gonadal function
- Controls corpora lutea formation in females
-Control testosterone secretion by interstitial cells of Leydig in males
-Need FSH to induce LH receptors in Leydig cells
-LH indirectly control spermatogenesis in males
47
classification of FSH
Controls follicular maturation in female ovary
- Production of estrogen
- Maturation of the oocyte
- Regulates differentiation of spermatogonia in males
48
What are three groups of anterior pituitary hormones
1) glycoproteins TSH, LH, FSH
2) Pro-opiomelanocortin (POMC)
3) Growth hormones and prolactin
49
classification of Proopiomelanocortin (POMC) Derivatives
ACTH and MSH
POMC is proprotein that includes peptide sequences for multiple hormones
-ACTH
-MSH
-Enkephalin
-Endorphin
Specific proteolytic enzymes packaged with the prohormone cleave off the activate hormone
-In corticotrophs ACTH is cleaved off POMC
-In melanotrophs MSH is cleaved off POMC
50
classification of corticotropin ACTH (Proopiomelanocortin (POMC) Derivatives)
- ACTH stimulates steroid biosynthesis within the adrenal cortex
- Controls production and release of glucocorticoids i.e. Cortisol and corticosterone
51
classification of posterior pituitary OXT AND AVP
Development and anatomy of the posterior pituitary
-Posterior pituitary results from the downward growth of neural ectoderm
-Posterior pituitary consists of neuronal terminals, blood vessels and pituicytes
-Pituicytes are neuroglial cells
-Axons that extend into the pituitary have cell bodies in the hypothalamus
-Cells bodies are part of the magnocellular system
-Cell bodies are located in two hypothalamic nuclei
SON: AVP predominates
PVN: OXT predominates
52
Control of posterior pituitary hormonal secretion
- Secretion requires activation of sensory receptors
- OT released in response to suckling and myometrial contraction
- AVP released in response to distension of vascular tissue
- Activation of receptors generate CNS signaling that activates neurons in SON and AVP
Depolarization of SON and AVP in response to neurotransmission generate action potentials
- Depolarization opens voltage-gated Ca2+ channels
- Ca2+ influx acts as a molecular trigger to initiate secretory granule exocytosis
53
Physiological roles of oxytocin
Two major functions in females
- Let-down reflex
- Uterine myometrial contraction during parturition (labor)
54
Milk release—Let-Down Reflex
| Physiological roles of oxytocin
Stimuli for release- Suckling of areola and nipple activates nerve endings
Through classical conditioning OT release can be associated with other stimuli i.e. sounds and smells associated with the infant
Location of OT receptors
-Alveoli of mammary glands are surrounded by myoepithelial cells
-OT receptors are located on myoepithelial cells
i-OT receptors when bound cause contractions of myoepithelial cells
-Alveolar secretory cells produce milk and are hormonally controlled by PRL
Expression of milk
- Contraction of myoepithelial cells compress underlying alveolae
- Compression pressurizes fluid within the alveolae and pushes it through the lactiferous duct
- Milk exits as a pressurized stream through a single pore
OT is only required for expression of milk
-Milk can be produced without OT
55
Milk release—Let-Down Reflex memorize
| Physiological roles of oxytocin
-baby suckling stimulates nerve endings in areola
-->
hypothalamus neural reflex is passed to pituitary gland via hypothalamus
-->
posterior pituitary
oxytocin contracts muscle wall of alveoli to release milk during feeding
-->
anterior pituitary
prolactin stimulates alveoli to produce breastmilk for future feedings
56
Uterine myometrial contraction during parturition
| Physiological roles of oxytocin
- OT is not required for the initiation of labor and pituitary OT may not be essential for its maintenance
- There is limited number of OT receptors in the myometrium prior to term
- OT receptor number and sensitivity increase during terminal stages of labor
- Number and sensitivity parallels estradiol and progesterone levels
- Progesterone inhibits OT myometrial receptor formation
- OT receptor formation and sensitivity increase with estradiol levels
- During late term pregnancy, ↓ progesterone and ↑ estrogen
******Pituitary OT causes myometrial contraction but primary source to initiate labor may be from direct uterine production*****
-OT in the uterus may primarily be a paracrine
-Rise of uterine OT concentration and OT receptor sensitivity may trigger labor
57
Effects of OT on human sexual response
| Physiological roles of oxytocin
OT levels increase during arousal and orgasm (male ejaculation) in both sexes
-Male sexual response
-AVP levels increase during arousal but return to baseline prior to ejaculation
-OT levels increase at the time of ejaculation in men- increase in OT causes increase in contractility of reproductive duct system
(Similar response in female reproductive duct system)
-Smooth muscle contraction of ducts increase egg and sperm transport
- Female sexual response
- Ovarian hormones increase firing rate of PVN during estrus (non-human)
- Estrogen causes an increase in OT release during genital stimulation
58
mechanisms of OT actions
****-OT interacts with myometrial and endometrial receptors
- Receptor binding stimulates the production of prostaglandin F2α
- Prostaglandins are local inflammatory agents that alter myometrial sensitivity*****
- Effects on uterine contraction
- OT binds receptors
- Receptor binding causes the release of intracellular Ca2+
- Ca2+ binds with and activates calmodulin (CAM)
- Ca2+ - CAM activates myosin light chain kinase
- Kinase phosphorylates myosin light chains (P–myosin)
- P-myosin binds with actin
- Binding with actin activates myosin ATPase
- Leads to molecular events associated with muscle contraction
59
Physiological roles of AVP
Two major functions
1. Regulation of blood pressure via control of smooth muscle contraction
2. Regulation of osmolarity via movement of solute and water across the DCT of the medullary nephron
- Increase absorption of water and Na+
60
AVP role in blood pressure
Physiological roles of AVP
↑ blood pressure → ↓ SON → ↓ AVP → increase urine output ↓ BP
-AVP release is also affected by renin – angiotensin – aldosterone mechanism
Angiotensin II → ↑ AVP → excretion of hypertonic urine → ↑ BP
Aldosterone → ↑ [Na+] → activation of osmoreceptors (OR) → ↑ AVP → excretion of hypertonic urine → ↑ BP
61
Mechanisms of AVP actions
Effect of AVP on movement of water across the DCT
- AVP causes the insertion of water channels in the apical surface of cells contacting the lumen of the DCT
- AVP binds receptors on the basal surface that contacts interstitial space
- Receptor activation increases cAMP
- cAMP activates a protein kinase
- PK induces migration of endosomal vesicles with AQP2— aquaporin
- AQP2—aquaporin is integrated into the membrane
- Water enters along concentration gradient
62
serotonin
5-HT
