baroreflex/dive refley

Question 1

What are the two main control systems for maintaining blood pressure?

Answer 1

The two main control systems for maintaining blood pressure are:

1. Local control of capillary flow, operated by chemoreceptors inside arterioles.
2. Nervous and endocrine control on the heart, arteries, and veins.

Question 2

Describe the mechanisms involved in tissue perfusion when metabolic activity increases.

Answer 2

When tissue becomes metabolically active, it consumes more oxygen and produces more carbon dioxide. This triggers two simultaneous mechanisms:

1. Local control: Chemoreceptors inside arterioles detect changes in oxygen and carbon dioxide levels, leading to the relaxation of capillary sphincters and arteriolar vasodilation.
2. Nervous control: This involves the autonomic nervous system, specifically the sympathetic and parasympathetic divisions, which regulate heart rate, arterial tone, and venous return to enhance blood flow to metabolically active tissues.

Question 3

How is the nervous system organized in bilateral animals, particularly in vertebrates?

Answer 3

In vertebrates, the nervous system comprises the central nervous system (CNS) and the peripheral nervous system (PNS), which further divides into:

1. Afferent division: Carries sensory information from receptors to the CNS.
2. Efferent division: Transmits instructions from the CNS to effector organs. It includes the somatic nervous system (SNS) and the autonomic nervous system (ANS), the latter further divided into sympathetic and parasympathetic divisions.

Question 4

Differentiate between sympathetic and parasympathetic nerve fibers based on their origins and neurotransmitters.

Answer 4

1. Sympathetic nerve fibers originate from nuclei in the thoracic and lumbar regions of the spinal cord. They release acetylcholine at preganglionic synapses and norepinephrine at postganglionic synapses.
2. Parasympathetic nerve fibers arise from nuclei in the brain stem and sacral region of the spinal cord. They release acetylcholine at both preganglionic and postganglionic synapses.

Question 5

What are baroreceptors, and where are they located in mammals?

Answer 5

Baroreceptors are specialized sensory nerve endings located in the aortic arch and carotid sinuses. They detect changes in blood pressure and stretch of arterial walls. Baroreceptors in the carotid sinuses are crucial for regulating blood pressure to the brain.

Question 6

Describe the physiological response during a hypertensive episode.

Answer 6

During a hypertensive episode, increased blood pressure triggers the activation of the parasympathetic nervous system. This leads to the release of acetylcholine, which decreases heart rate through muscarinic receptors in the SA node, ultimately reducing blood pressure.

Question 7

Explain the physiological response during a hypotensive episode.

Answer 7

In a hypotensive episode, the sympathetic nervous system is activated, leading to the release of norepinephrine. Norepinephrine increases heart rate, myocardial contractility, and vasoconstriction, ultimately raising blood pressure.

Question 8

What are the main types of adrenergic receptors involved in blood pressure regulation?

Answer 8

The main types of adrenergic receptors are:

• α1 receptors (activators)
• β1 receptors (activators)
• α2 receptors (inhibitors)
• β2 receptors (inhibitors)

Their activation or inhibition influences vascular tone and cardiac function, thereby affecting blood pressure.

Question 9

How is blood volume regulated in the body?

Answer 9

Blood volume is primarily regulated by renal mechanisms, including direct and indirect controls.

1. Direct control involves atrial stretch receptors releasing atrial natriuretic peptide (ANF) to increase diuresis and sodium excretion.
2. Indirect control involves osmoreceptors in the hypothalamus regulating vasopressin secretion to adjust water reabsorption and diuresis.

Question 10

What is the dive reflex, and how does it function in marine mammals?

Answer 10

The dive reflex is an adaptation in marine mammals that redirects blood flow to vital organs during prolonged submersion. It involves

1. arteriolar vasoconstriction
2. bradycardia (decreased heart rate)
3. and increased vasoconstriction mediated by chemoreceptors and mechanoreceptors

ensuring oxygen supply to essential tissues during diving.

Question 11

Name some adaptations in marine mammals for prolonged submersion.

Answer 11

Marine mammals such as seals have adaptations including
- increased blood volume
- high hematocrit values
- a well-developed heart
- elastic aortic bulbus and retes mirabilis to buffer pressure changes and prevent decompression sickness

Question 12

What neurotransmitters are involved in the autonomic nervous system, and how do they differ in their effects?

Answer 12

1. Acetylcholine: Released by both sympathetic and parasympathetic preganglionic fibers. In the sympathetic nervous system, it binds to nicotinic receptors at ganglia, while in the parasympathetic system, it binds to nicotinic receptors at ganglia and muscarinic receptors at target organs. Overall, acetylcholine mediates synaptic transmission.
2. Norepinephrine: Released by sympathetic postganglionic fibers. It primarily binds to adrenergic receptors at target organs, exerting excitatory effects.

Question 13

What are the main roles of α1 und 2 and β1 und 2 adrenergic receptors in blood pressure regulation?

Answer 13

• α1 receptors: Activators that primarily bind to norepinephrine, causing vasoconstriction when stimulated.
• α2 receptors: Inhibitors that primarily bind to norepinephrine, modulating neurotransmitter release and contributing to blood pressure regulation.
• β1 receptors: Activators that equally bind to norepinephrine and epinephrine, increasing heart rate and contractility when stimulated.
• β2 receptors: Inhibitors that primarily bind to epinephrine, causing vasodilation when stimulated.

Question 14

Describe the direct control mechanism for regulating blood volume.

Answer 14

• atrial stretch receptors detecting changes in blood volume
• Excessive blood volume triggers the release of atrial natriuretic peptide (ANF) into the bloodstream
• ANF acts on the kidneys to inhibit the secretion of renin and aldosterone
• leading to increased diuresis and sodium excretion
• thereby reducing blood volume and pressure

Question 15

Describe the indirect control mechanism for regulating blood volume.

Answer 15

• involves osmoreceptors in the hypothalamus
• monitoring intercellular water levels
• Increased water levels suppress vasopressin (antidiuretic hormone) secretion from the posterior pituitary gland
• Reduced vasopressin levels decrease water reabsorption in the kidneys
• promoting diuresis and reducing blood volume and pressure

Question 16

What role do chemoreceptors and mechanoreceptors play in the dive reflex?

Answer 16

1. Chemoreceptors in the aortic arch and carotid sinuses detect changes in blood oxygen, carbon dioxide, and pH levels, signaling the body to adjust heart rate and vascular tone to ensure adequate oxygen supply.
2. Mechanoreceptors in the oral and nasal mucosa sense pressure changes during diving, triggering reflex responses in the cardiovascular and respiratory centers to optimize oxygen utilization and conserve energy.

Question 17

Name some specialized adaptations in marine mammals for prolonged submersion.

Answer 17

1. Weddell seals have adaptations such as increased blood volume, high hematocrit values, a well-developed heart, elastic aortic bulbus, and retes mirabilis to buffer pressure changes and prevent decompression sickness.
2. Cetaceans possess retia mirabilia, networks of vessels that help regulate blood flow and prevent nitrogen bubble formation during deep dives.

Question 18

What are the three major steps involved in hemostasis?

Answer 18

1. Vascular spasm: Vasoconstriction of damaged blood vessels initiated by serotonin and angiotensin II, followed by vasodilation mediated by histamine and prostaglandins to facilitate repair.
2. Formation of the platelet plug: Platelet aggregation and adhesion to the injured vessel wall, triggered by exposure of collagen. Platelets release ADP and vasoconstrictors like serotonin and thromboxane A2, while intact endothelium releases prostacyclin and NO to limit plug size.
3. Blood coagulation (clotting): Activation of the coagulation cascade, leading to the conversion of fibrinogen to fibrin, stabilization of the platelet plug, and formation of a blood clot.

Question 19

Describe the intrinsic pathway of blood clotting.

Answer 19

• The intrinsic pathway involves seven steps and leads to blood clotting within damaged vessels without significant bleeding.
• It is initiated by factors within the bloodstream, eventually activating prothrombin to thrombin, which then converts fibrinogen to fibrin for clot formation.

Question 20

Explain the extrinsic pathway of blood clotting.

Answer 20

• The extrinsic pathway consists of four steps and leads to the coagulation of blood that has escaped from damaged tissues, causing significant bleeding.
• It is initiated by tissue factor (factor III) released from damaged tissues, triggering a cascade that leads to thrombin activation and fibrin formation.

Question 21

What are the main effects of thrombin during blood clotting?

Answer 21

Question 22

Describe the process of clot dissolution.

Answer 22

• Clot dissolution begins simultaneously with clot formation but proceeds slowly.
• Exposed collagen at the site of injury triggers platelet aggregation and clotting cascades, which are rapid mechanisms.
• Concurrently, plasmin is activated, slowly dissolving the clot over time once it is no longer needed for repair.

Question 23

How do anticoagulants prevent or delay blood clot formation?

Answer 23

• Anticoagulants prevent or delay blood clot formation by inhibiting various steps of the coagulation cascade.
• Examples include heparin (a thrombin inhibitor), citrate, EDTA (which bind free calcium ions necessary for coagulation), lamphredin (affecting fibrinogen), and hirudin (another thrombin inhibitor).