regulation of visceral activity4

8/6/2019 Regulation of Visceral Activity4

1/54

REGULATION OF VISCERALACTIVITYWAYNE MANANA

BDS(UZ),BA,MDS(OMFS)

FACILITATOR ; DR W. MURITHI


2/54

COMPONENTS OF A CONTROLLED

SYSTEM

sensor

Afferent pathway

Controller/ intergrator Efferent pathway

Effector

Controlled variable


3/54

Mechanisms of visceral activity control

Can be

Negative feedback(most common)

Positive feedback e.g release of cck, secretin

Feedforward e.g exercise, salivation, gastric secretion


4/54

Can also be

Involuntary/ automatic

voluntary

Can be

Endocrine

Paracrine

Neuronal/ nervous


5/54

Major visceral activity

Cardiovascular system

Respiratory system

Gastrointestinal system Renal system

Genitourinary system


6/54

LEVELS OR HIERACHY OF

REGULATION

Spinal cord

Bladder reflexes

Medulla(vital centres)

CVS and RS

Vomiting, coughing, gagging, sneezing, swallowing

Hypothalamus

Satiety, hunger, thirst, Midbrain-pupillary and accommodation reflexes

Basal nuclei and cortex-modulation of brain stem


7/54

Spinal cord(defecation/voiding)


8/54

MEDULLARY LEVEL

REGULATION OF CVS

Can be

Neural(rapid pressure changes e.g postural changes)

Endocrine( delayed response)

paracrine

Regulation occurs at

Local tissue level(autoregulation)

Systemic/ general


9/54

CONTROLLED VARIABLES

Blood pressure

Oxygen and nutrients to the tissues

Carbon dioxide, H+, metabolites from tissues

Temperature(thermoregulation)


10/54

Receptors cvs

Baroreceptors

Stretch receptors in the tunica adventia

High pressure baroreceptors

Carotid sinus Aortic arch receptors

Low pressure baroreceptors(cardiopulmonaryreceptors)

Rt and lt atrium(Type A and Type B) receptors Pulmonary vessels receptors

Ventricular walls


11/54

Baroreceptors cont

More sensitive to pulsatile pressure than to constant

pressure

Chronic hypo/hypertension resetsthe

baroreceptors

Carotid sinus- linear relationship in response

between 70 and 150mmHg


12/54

chemoreceptors

Peripheral chemoreceptors mainly exert their effect

on resp system but their stimulation also causes

vasoconstriction

Hypoxia produces hyperpnea and increases

catecholamine release


13/54

Afferent pathway

Carotid sinus

Glossopharyngeal(carotid sinus nerve)

Aortic arch

Vagus(aortic depressor nerve)

Neurotransmitter

glutamate


14/54

Basic pathways; medullary bp control


15/54

Medullary control of heart rate by

vagus


16/54

Other afferents to th RVLM

excitatory

Limbic cortex that relay in the hypothalamus

Mesencephalic periaquaductal gray

Brainstem reticular formation

Pain pathways

Somatic afferent(somatosympathetic reflex..exercise)


17/54

Afferent cont..

Inhibitory

Cortex via hypothalamus

Caudal medullary raphe

Lung inflation afferents


18/54

Efferent and effector

ANS to smooth muscles(mainly arterioles) via

endothelial cells

Ach binds to end cells and they is increased

intracellular calcium which activate NOS3 which

activates guanyly cyclase then relaxation smooth

muscle

Expt capillaries and venules Noradrenegic expt muscles

Cardiac receives both PS and S


19/54

autoregulation

Myogenic theory of autoregulation

Metabolic theory of autoregulation

Stagnation built-up of metabolites

Metabolites have vasodilator effect e.g low O2, Low

pH, inreases CO2, hyperosmolarity, rise in temp,

hyperkalaemia a feature, lactate, histamine, adenosine,

NO(EDRF),bradykinin, CO

vasoconstriction 5-HT from plts in injured,histamine via

H1, sub P, VIP, ET


20/54

REGULATION OF RS

Can be voluntary or involuntary

Can be neuronally or chemically controlled

The controlled variable is pO2, pCO2 and pH


21/54

chemoreceptors

Chemoreceptors

Carotid bodies (more important)

Aortic bodies

Medullary chemoreceptors(R/CVM)

Close to NTS,hypothalamus, locus ceruleus

Glomus cells(type 1) with K+-sensitive O2

channels and L-type Ca2+ channels Stimulated by low O2, CN-,nicotine, lobeline,

hyperkalaemia,


22/54

Non-chemical receptors

Myelinated

Slow adapting type(herring-breuer relexes)

Rapidly adapting type(irritant receptors)

Non-myelinated(J receptors)

Pulmonary C fibers

Bronchial C fibers


23/54

afferent

Afferent Vagus (aortic body and the non-chemical receptors)

Glossopharyngeal (carotid body)

Have D2 receptors


24/54

contollers

4 contollers

Pre-BOTC

Dorsal and Ventral

groups of resp

Pneumotaxic centre


25/54

DRG and VRGbothfound in the medulla andproject to the pre-BOTC

Pneumataxic center

modifies the Pre-BOTC.PC located in the medialparabrachial and kollikernuclei of th dorsolat pons

PC fxn not known butprobably switchingbtwn insp and exp


26/54

OTHER AFFERENTS

Reticular formation

Propioceptors

Limbic system, hypothalamus

Baroreceptors

Cerebral cortex


27/54

efferents

Voluntary

Corticospinal to accesory muscles of resp and

intercostal muscles

Automatic

Cervical via phrenic nerve goes to the diaphragm

Thoracic via intercostal nerves goes th intercostal

muscles

Sympathetic(B2) causes brochodilation & vasoC

Parasymp(vagus) opposes symp


28/54

COUGHING AND SNEEZING

Triggered my irritation of resp mucosa

Coughing begins by deep insp followed by forced

exp.

Intrapulmonary pressure increases to 100mmHg or

more, glottis open, outflow at 965km/hr(600mi/hr)

Sneezing similar expt glottis continuosly open and

initiated by pain fibers of trigeminal nerve(nasalepithelium)


29/54

REGULATION OF GIT

Regulation can be

neural,(intrinsic and extrinsic)

endocrine and paracrine

Controlled variable is secretion and motility with an

ultimate goal of efficient digestion, absorption and

assimilation

Git like the little brain


30/54

Regulation of salivation(prototype for

glands)

Feed forward andfeedback

Symp alpha-1causes thick viscous,Beta causesamylase secretion


31/54

vomiting


32/54

HYPOTHALAMUS LEVEL


33/54


34/54

VISCERAL FUNCTION OF

HYPOTHALAMUS


35/54

FUNCTIONS CONT..


36/54

Role of hypothalamus in;

Posterior pituitary(oxytocin/VP)

Appetitive mechanisms

Hunger and satiety

thirst

Relation to

Autonomic function

Cyclic phenomenon


37/54

HUNGER AND SATIETY

Appetite depends on interaction btwn

Satiety centre(ventromedial nucleus)

Feeding centre(bed nucleus of forebrain bundle at its

junction with the pallidohypothalamic fibres)

Leptin and more 20 proteins/pptides have been

implicated in the regulation of appetite


38/54

HUNGER AND SATIETY


39/54

AFFERENT MECHANISMS HYPOTHESIS

Lipostatic hypothesis

Humoral signal(leptin) from adipose produced

proportional to fat, acts on hypoTh to inhib apt

Gut peptide hypothesis

Food in GIT stimulates hormones to inhib hypoTh

Glucostatic hypothesis

Thermostatic hypothesis Fall in temp below set pt stimulate apt and vice versa


40/54

LEPTIN (lipostatic hypothesis)

167aas, o/b gene(leptin)and d/b gene(receptor)

Acts on the hypoTh todecrease food intake by

Decrease th activity ofneuropepptide Y neurons

Increase th activity of POMCfrom neurons

Leptin acts on arcuate

nuclei(can be destroyed bygold thioglucose)

Competes for CB1 receptorwth cannabinoids


41/54

GHRELIN

28 aas pptide wth n-

octanyl on serine 3

residues

Antagonizes the action ofleptin

Produced by stomach to

act on th arcuate nuclei to

stimulate appetite

Stimulates GH release


42/54

Other peptides

Peptide YY3-26(PYY)

From small intestines and colon to inhibit appetite

GIT hormones

CCK, secretin, somatostatin, gastrin, GRP


43/54

THIRST

Triggered by hypovolaemia

hyperosm

Psychological

Osmoreceptors located in thant hypoTh in thcircumventricular organs

subfornical organ and OVLThave receptors forAngiotensin II

Baroreceptor reflexmechanisms also involved intriggering thirst in

hypovoelemic patients


44/54

Thirst-osmolarity relationship


45/54

Other factors affecting water intake

Prandial water drinking

Psychological/ habit

Increased plasma osmolarity

GIT hormones acting on the hypothalamus

Ant cerebral artery injuries,lesions in the ant hypoTh,

altered state of unconsciousness, high protein diet,

pharyngeal mucosa drying Pharyngeal gastrointestinal metering probably

involved in satisfaction of thirst


46/54

CONTROL OF POST PITUITARY FXN

OXYTOCIN AND VASOPRESSIN Nonapptides neural hormones

with terminal disulphide ring

Synthesized by magnocellularneurons(Herring bodies

granules) in theparaventricular and supra-optic nuclei

Other species have lysine-VP

Also found in gonads,

thymus,adrenal cortex,suprachiasmatic N, brainstem& spinal cord(T.boutons)


47/54

CHEMISTRY OF VP AND OXYTOCIN

An AP in the magnocellular neurons triggers a Ca2+

mediated exocytosis of both VP and oxytocin


48/54

Physiologic action of VP

Release is phasic bursting non-synchronous and

mantains a prolonged output increase in VP

Causes water retention in excess of solute by acting

on collecting duct

VIAReceptors

G protein coupled to increase IC Ca2+ and mediates

vasoC.(at high levels because at low level causes adecrease in CO by acting on th area postrema)

Also found in the liver(glycogenolysis), brain&cord(NT)


49/54

Receptors cont

V1B(also calledV3)is a G protein coupled to

increase IC Ca2+ found in the ant pituitary to

release ACTH.

V2 receptor

is a Gs protein coupled that triggers to increase cAMP

found on the principal cells of the collecting duct

Facilitates insertion of aquaporin-2 into the apicalmembrane


50/54

Relationship btwn osm/BP and VP


51/54

VP

T1/2 of18mins andinactivated in the liver

Regulated by OVLT

receptors but the

threshold for thirst is

slightly higher

Significant changes

occur even if osmchanges by 1%


52/54

oxytocin

Acts via G protein coupled receptors on themyometrium, breast myoepithelial cells and ovary totrigger increase in I.C Ca2+ .

Milk ejection reflex(neuroendocrine reflex)Many hormones cause breast growth and secretion but

ejection is entirely due to oxytocin

Tactile/stretch receptors on the nipple trigger a high

frequency, synchronous discharge of Oxytocin Emotions and genital stimulation stimulate release but

alcohol inhib


53/54

Other actions of oxytocin

Stimulate uterine contraction. Inhibited by

progesterone(competitive inhib on oxytocin

receptors) and activated by estrogen

Coitus stretch stimulate uterine contraction tofacilitate mvnt of sperm.

circulating levels elevated at ejaculation ???

contraction of vas deferens smooth muscle??


54/54

QUOTE OF THE DAY

WHAT IS NOT WORTH DYING FOR IS NOT

WORTHY LIVING FOR

HYPOTHALAMUS REGULATES BUT GOD

CONTROLS

regulation of visceral activity4

Documents