Fisiologia Flashcards
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Estômago
O bolo alimentar ao atingir o estômago vai distendê-lo. Esta distensão é sentida por
______________(1) na camada ____________(2) que vai levar à libertação de __________(3) pelas células _____(4) no estômago.
Esta hormona, por sua vez, promove a secreção de _______________(5) pelas células _____________(6) e ______________(7) pelas células _____________(8) e induz a contração das células musculares gástricas.
1 - mecanorrecetores
2 - submucosa
3 -gastrina
4 - G
5 - HCl (ácido Cloridrico)
6 - parietais
7 - pepsinogénio
8 - chefe
Qual o sistema nervoso que controla a taxa de contração do estômago (geralmente 4 contrações por minuto)?
Sistema Nervo Entérico
Myenteric plexus - Short reflex arc
*Concerns with the contractility and motility of the stomach
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Estomago
Na membrana da célula existe a bomba H+K+ ATPase, onde há saída de ________(1) para o __________(2) das glândulas gástricas, com a troca de __________(3) para o seu interior, num processo de transporte ativo. Este último, sofre constantemente reciclagem, passando para o lúmen das glândulas gástricas por canais de _________(4);
Na membrana celular, há outra bomba, a Na+K+ ATPase, que bombeia o __________(5) para fora da célula e o ___________(6) para dentro da célula, aproximadamente 3 _________(7) e 2 ___________(8).
1 - Hidrogénio (H+)
2 - lúmen
3 - Potássio (K+)
4 - Potássio (K+)
5 - sódio (Na+)
6 - potássio (k+)
7 - Sódios (NA+)
8 - Potássios (K+)
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Estômago
Existem muitas mitocôndrias na célula parietal, o que as torna dependentes de oxigênio. Como resultado da respiração celular, será produzido _______________(1). Este, juntamente com H2O, pela ação da _______________(2), produz ______________(3). Este último, dissocia-se em H+ e __________(4).
Os protões (H+) irão para o _________(5), através da bomba de protões e o ___________(6) vai para os vasos sanguíneos, com a troca de ___________(7), para o interior da célula. Este passará pela célula parietal apenas para ser empurrado para o ________(8) através de canais especiais.
No lúmen, agora, há íões de ___________(9) e íões de _____________(10), isso formará ________________(11).
1 - dióxido de carbono (CO2)
2 - anidriase carbónica
3 - ácido carbónico (H2CO3)
4 - HCO3- (bicarbonato)
5 - lúmen
6 - bicarbonato
7 - Cloreto (Cl-)
8 - lúmen
9 - hidrogênio(H+)
10 - cloreto (Cl-)
11 - ácido clorídrico (HCI)
Vagus nerve stimulates the parietal and chief cells to
make hydrochloric acid and pepsinogen →
pepsinogen at an optimal pH of 1.8-3.5 can be
activated to a digestive enzyme known as pepsin
Complete:
Nervous System Stimulation
________________(1) stimulation increase the gastric acid release;
________________(2) stimulation decrease the gastric release by inhibition of _________(3) nerve stimulation.
1 - Parasympathetic
2 - Sympathetic
3 - vagal (Parasympathetic)
Explain the Vasovagal reflex
Stretch receptors at the muscularis externa of the stomach is stimulated by the food occupying the stomach → this activates different types of reflexes including:
The Vagovagal reflex
Long reflex arc
- Stretch receptors are coupled with afferent fibers of cranial nerve 10 (vagus nerve) which is a sensory nerve → sends signals to nervous system
- The efferent nerves which reach the stomach sends signals away from the nervous system
- Stretching of the stomach stimulates the vagus nerves (stimulates the parietal and chief cells)
How does the Partially digested proteins stimulates the gastrin hormone secretion?
- Directly related to pH
o Proteins are buffers which has specific sequences
o Amino acids which make up the protein have negative charges that can tie up protons
o When there’s a lot of proteins:
->pH which is initially low (a lot of protons)
->increase the pH
->inhibit the conversion of pepsinogen into pepsin - Enteroendocrine G cells in the gastric glands of the antrum → responds to partially digestive proteins:
- Increase in the partially digestive proteins in the gastric mucosa stimulates enteroendocrine G cells → this secretes gastrin hormone → which travels through the
blood.
How does the gastrin, secreted by the enteroendocrine G cells stymulates the gastric acid secretion?
Gastrin hormone → which travels through the
blood:
(i) It reaches the parietal cells: Bind to cholecystokinin type 2 (CCK 2) receptor, which is a natural peptide on parietal cell
-> Increase intracelular calcium
-> Stimulate protón pump on the parietal cell
-> Pushes hydrogen(protons) out of the lumen and brings the potassium into the lumen
-> The environment becomes concentrated with protons (acidic) which is the component of hydrochloric acid
(ii) Reaches the chief cell (Which can be found throughout the stomach): Gastrin binds onto cholecystokinin type 1 (CCK1) receptor on the chief cell
-> Stimulate vesicles in the chief cell to fuse with the cell membrane
-> Exocytosis like pocket with pepsinogen molecules
o when there’s a proper concentration of protons, optimally pH around 1.8-3.5 can stimulate conversion of pepsinogen to pepsin
o Hence, hydrochloric acid is needed to activate this
What is the primary inhibitor of gastric secretion?
Sympathetic nervous system
o Stress
o Emotional upset
o Anxiety
o Depression
This is achieved through:
- Stimulation of sympathetic preganglionic fibers in the spinal cord (T1-L2)
-> which gives impulses through greater splanchnic nerves and reaches the stomach
-> inhibit parasympathetic nervous system
-> this inhibits hydrochloric acid release and pepsinogen release
Somatostatin is secreted with the Stimulus of Really low pH/high amounts of protons intraluminal (lumen of the stomach). What is the Mechanism?
o Antral D-cell in the antrum of the stomach which is a chemoreceptor and a hormone, detects the high concentration of the proton
-> secretes somatostatin into the blood
-> somatostatin acts on nearby cells (paracrine)
-> binds to somatostatin receptor on the antrum of the stomach
-> this inhibits the G-cells from releasing gastrin
o Gastrin that was initially responsible for stimulation of pepsin and proton secretion will be inhibited
-> the high amounts of hydrochloric acid in the stomach will be lowered
O que estimula a libertação de somatostatina nas células D do antro?
pH diminuido (ácido)
O que inibe a libertação de somatostatina nas células D do antro?
Nervo vago (acetilcolina)
Gastrina (G)
O que estimula a libertação de gastrina nas células G do antro?
Nervo Vago
Muitas proteinas (aumento do pH)
O que inibe a libertação de gastrina nas células G do antro?
Somatostatina
