Homeostasis and Its Mechanisms

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Questions and Answers

Which blood group contains both A and B agglutinogens?

Group AB (correct)

Group A

Group O

Group B

What type of antibodies are agglutinins against A and B agglutinogens?

IgA

IgE

IgM (correct)

IgG

What condition may result from Rh incompatibility between mother and fetus?

Thalassemia

Erythroblastosis Fetalis (correct)

Sickle-cell Disease

Polycythemia

How frequently do Rh-positive individuals express the D antigen?

85 – 90% (A) Signup and view all the answers

What is an essential treatment for newborns affected by severe Rh incompatibility?

Exchange transfusion (B) Signup and view all the answers

Which blood group does not contain any A or B agglutinogens?

Group O (A) Signup and view all the answers

What triggers the formation of anti-D agglutinin in Rh-negative individuals?

Injection with Rh-positive cells (C) Signup and view all the answers

Which group of antibodies are formed 3-6 months after birth against non-expressed agglutinogens?

IgM and IgG (C) Signup and view all the answers

What is the primary role of somatic sensory fibres?

To relay sensations of pain, temperature, and touch (A) Signup and view all the answers

Which statement about autonomic and somatic nervous systems is accurate?

Autonomic system can be both excitatory and inhibitory (C) Signup and view all the answers

Which spinal nerve has a purely motor function?

C1 (A) Signup and view all the answers

From where do somatic efferent motor spinal nerves arise?

From all spinal cord segments (C) Signup and view all the answers

What is the resting membrane potential (RMP) in excitable tissues typically range between?

-70 to -90 mV (D) Signup and view all the answers

What is the primary function of a dermatome?

Supplying a skin area with sensory nerves (D) Signup and view all the answers

What characterizes the outer and inner surfaces of a cell membrane at resting membrane potential?

The outer surface is positively charged while the inner is negatively charged (A) Signup and view all the answers

Which autonomic efferent fibers arise from the middle sacral segments?

Parasympathetic (D) Signup and view all the answers

What is the main consequence of continuous potassium efflux through transmembrane protein channels?

Accumulation of positive charges outside the cell (B) Signup and view all the answers

What is the primary characteristic of fatty change, or steatosis, in cells?

Abnormal accumulation of fat inside cells (D) Signup and view all the answers

Which organ is NOT commonly affected by fatty change?

Lungs (D) Signup and view all the answers

What is the role of the sodium-potassium pump in maintaining membrane potential?

It extrudes 3 sodium ions and intrudes 2 potassium ions (C) Signup and view all the answers

Which of the following can cause fatty change in cells?

Bacterial toxins (C) Signup and view all the answers

During depolarization, what happens to the sodium ion channels?

They open, allowing sodium influx (A) Signup and view all the answers

What mechanism allows action potentials to propagate in unmyelinated nerves?

Self-propagation through local current flow (A) Signup and view all the answers

What is the main distinction between necrosis and apoptosis?

Necrosis involves local death of cells, while apoptosis is regulated cell death. (C) Signup and view all the answers

What does the term 'lipomatosis' refer to?

Localized accumulation of fat without obesity (B) Signup and view all the answers

In myelinated nerves, what is the primary mode of action potential propagation?

Saltatory conduction at the nodes of Ranvier (D) Signup and view all the answers

What is one advantage of saltatory conduction?

It uses less ATP compared to non-myelinated propagation (A) Signup and view all the answers

What is a common feature of 'signet ring cells' encountered during the microscopic examination of cells with fatty change?

Fat globules that push the nucleus to one side (B) Signup and view all the answers

Which condition is associated with obesity due to hormonal disturbances?

Lipomatosis (D) Signup and view all the answers

What occurs during the repolarization phase of an action potential?

Increased potassium permeability with potassium efflux (D) Signup and view all the answers

What is the significance of mucoid degeneration?

It involves the accumulation of mucin within epithelial cells. (A) Signup and view all the answers

Where do T cell progenitor cells develop after leaving the bone marrow?

Thymus (C) Signup and view all the answers

Which of the following are acute immune transfusion reactions?

Anaphylaxis (A), Acute hemolytic transfusion reactions (C) Signup and view all the answers

What is a major cause of morbidity and mortality in patients with transfusion-dependent diseases?

Iron Overload (C) Signup and view all the answers

What is the recommended temperature for storing blood in blood banks?

4º C (B) Signup and view all the answers

What occurs when agglutinated RBCs block capillaries during an acute transfusion reaction?

Pain and tightness of the chest (B) Signup and view all the answers

Which precaution is not necessary before a blood transfusion?

Freezing the blood (D) Signup and view all the answers

What is a possible delayed reaction to blood transfusion?

Transmission of diseases (C) Signup and view all the answers

What complication can arise from mechanical overloading of the circulation during a blood transfusion?

Cardiac distress (D) Signup and view all the answers

What substance is used to prevent blood from clotting during storage?

Acid citrate (C) Signup and view all the answers

What effect does the positive feedback loop generated by thrombin have on coagulation?

It amplifies the production of thrombin. (C) Signup and view all the answers

Which of the following is NOT a natural anticlotting mechanism?

Activation of factor VIIa by tissue factor. (C) Signup and view all the answers

Which condition is a main indication for recombinant t-PAs?

Myocardial infarction. (C) Signup and view all the answers

What is the role of anti-thrombin III in the coagulation process?

It inactivates several clotting factors. (C) Signup and view all the answers

What is the role of tissue factor pathway inhibitor (TFPI) during coagulation?

It prevents the initiation of coagulation. (D) Signup and view all the answers

Which of the following factors does not get inactivated by anti-thrombin III?

Factor VII. (D) Signup and view all the answers

What does the template bleeding time measure?

The time required for bleeding to stop. (C) Signup and view all the answers

What could potentially cause a prolonged bleeding time?

Thrombocytopenia. (B) Signup and view all the answers

Study Notes

Homeostasis

Cells function optimally when the correct concentrations of extracellular fluid (ECF) components are present.
ECF is the body's internal environment.
Homeostasis maintains a stable internal environment.
Key components of homeostasis include: variable, sensor, integrator, and effector.

Homeostatic Mechanisms

Stability within a system is a result of measuring change (variation). The system detects errors and counteracts them to maintain balance.
To achieve this, we need variable, sensor, integrator and effector.

Components of Homeostatic Mechanisms

Receptors are sensors that detect changes in the environment (internal and external) and transmit the information.
Receptors are frequently nerve cells that send information about changes in the controlled variable via frequency of action potentials. These sensors are often specialized ion channels.
A controller (or integrator) receives the signal/input from sensors, compares the input to a set point and sends a corrective signal if needed.
Effectors respond to the integrating center's signals to correct any errors and bring the variable back to its set point.

Types of Feedback

Negative feedback: A change in the variable elicits a response to restore the variable to the set point. An example of negative feedback is blood glucose.
Feed-forward: Events respond anticipatorily to a stimulus. An example of feed-forward is increased thirst when eating salty food.
Positive feedback: A change in the variable elicits an even greater change in the same direction. Examples of positive feedback are blood clotting and childbirth.

Levels of Control

Whole body response: Involves autonomic nervous system, endocrine system, and behavioural responses (ionic balance, blood pressure, blood volume).
Local response: Organ-specific actions, such as constriction of blood vessels in the lungs when low oxygen levels are detected.
Cellular response: When a nerve cell becomes activated and depolarised, potassium channels open to restore the resting membrane potential.

Membrane Transport

Passive transport: Movement of molecules across a membrane without energy input. Includes simple diffusion (molecules move down their concentration gradient) and facilitated diffusion (molecules move down their concentration gradient with the help of protein channels).
Active transport: Requires energy input to move molecules against their concentration gradient.

Osmosis

Movement of water across a semi-permeable membrane from a solution of lower osmolarity to a solution of higher osmolarity until equilibrium occurs.
Osmolarity is the number of osmoles of solute per liter of solution, reflecting the number of dissolved particles and therefore the water concentration.

Hypertonic, Hypotonic, and Isotonic Solutions

Hypertonic: Higher osmolarity outside the cell; water moves out of the cell, causing cell shrinkage.
Hypotonic: Lower osmolarity outside the cell; water moves into the cell, causing cell swelling.
Isotonic: Equal osmolarity inside and outside the cell; no net change in water movement, resulting in no change in cell volume.

Molarity and Osmolarity

A mole of a substance has a mass in grams equal to its molecular weight.
Molar concentration is the number of moles of a substance per litre.
One osmole is the number of moles of a substance that contributes to osmotic pressure.
Osmolarity is the sum of the molar concentration of all the solutes.

Cell Permeability

Movement of water across a semi-permeable membrane from lower osmolarity to higher osmolarity.

Obesity

A complex disorder with multiple etiologies, characterised by excess body fat threatening socioeconomic, mental, or physical health.
Types of obesity include android and gynoid.

Obesity Measures

Skin fold measurements: Measuring skin folds at various body sites to estimate body fat percentage.
Body Mass Index (BMI): A simple index of body fat calculated using weight and height.
Calculation of BMI: weight (kg)/ height (m)^2.
Waist circumference: Measurement of the waist to assess abdominal fat.
Waist/hip ratio: Measurement of the waist and hip to indicate the distribution of body fat.

Treatment of Obesity

Dietary recommendations: Caloric restrictions (1200-1500 calories/day), low-carb diets, high protein, fat, and fiber intake.
Physical activity: Regular physical activity to enhance weight loss and prevent weight gain.
Pharmacotherapy: Medications to enhance satiety, decrease fat absorption, increase energy expenditure, decrease appetite.
Surgery: Bariatric surgery for individuals with significant obesity and comorbidities (BMI > 40 or BMI > 35 with associated conditions). The criteria are BMI >40 or BMI > 35 with associated health conditions.

Physical Activity

Defined by its duration, intensity, and frequency. Regular physical activity involves activities performed in an organised way, with the chosen intensity dictating the frequency.

Exercise vs. Sports

Exercise is physical activity aimed at improving health and fitness.
Sports are complex, institutionalized, and competitive forms of exercise.

Benefits of Exercise

Weight control. Reducing feelings of depression and anxiety.
Increased ability to perform daily tasks. Improvements in work performance.
Healthy bones, muscles, and joints.
Enhanced cardiovascular function and reduction in cardiovascular diseases.
Reduced risk of colon cancer.
Reduced blood pressure in people with high blood pressure.
Mitigating effects of age and improved health for a longer time.

Action Potentials

Action potential results from a rapid sequence of changes in the membrane potential.
Depolarization occurs due to the influx of sodium ions. Re-polarization occurs due to the efflux of potassium ions.

Chemical Synapses

A chemical synapse is a junction between two neurons. When transmitted from one neuron to the next, the electrical signal converts to a chemical signal. This chemical signal then causes more electrical signals in the next neuron.
Neurotransmitters are chemical messengers that carry the signal across the synaptic cleft between neurons.

Blood Cell Development

Blood cells develop from hematopoietic stem cells. The stages are detailed in the provided document.

Receptors

Receptors are protein-based cells that detect changes in their external environment.
Receptors may include nerves that relay sensations of pain, temperature, and touch.

T-Cells

T-cells are lymphocytes involved in the immune response—they have a variety of roles within the immune system.

B-Cells

B-cells are lymphocytes that play a vital role in the immune system.

Monocyte-Dendritic Cell Lineage

Monocytes act as antigen-presenting cells, triggering an immune response to foreign intruders.
Monocytes develop into macrophages to engulf foreign pathogens.

Macrophage

Macrophages are antigen-presenting cells that aid in inflammatory processes and wound healing. They also play a key role in phagocytosis (engulfing foreign particles).

Dendritic Cells

Dendritic cells are antigen-presenting cells that patrol tissues, seeking out and presenting foreign invaders to the immune system.

Neutrophils

Neutrophils are white blood cells that fight infection by killing and digesting bacteria and fungi.

Neutrophil Disorders

Both neutropenia (low neutrophil count) and neutrophilia (high neutrophil count) are classified as neutrophil disorders, which are caused by viral and bacterial infections, certain medications and cancers.

Eosinophils

Eosinophils are involved in the immune response to certain pathogens, such as parasites, and in reactions to allergies and asthma, by releasing various factors to mediate the immune response.

Basophils

Basophils are specialized white blood cells, crucial to the immune response, known for releasing histamine in allergic reactions and contributing to immediate hypersensitivity reactions to foreign particles.

Mast Cells

Mast cells are granulated cells that play a key role in the immune system, particularly in mediating inflammation and allergic responses, releasing various factors including histamine.

Homeostasis (blood)

Haemostasis involves mechanisms to prevent blood loss, keep blood within vessels. It involves interaction between the blood vessels, platelets, and coagulation factors.

Vasoconstriction

Nervous reflexes caused by pain impulses due to trauma. This results in contraction of the nearby injured blood vessels.
Local myogenic spasm caused by direct damage to the vascular wall and release of local substances such as thromboxane A2 & serotonin from traumatized tissues and platelets.

Primary Haemostasis

Injured blood vessel → Collagen exposure → Platelet adhesion to collagen → Platelet activation & degranulation → Platelet aggregation → formation of initial platelet plug.

ADP & Thromboxane A2

ADP causes platelets to become sticky, promoting platelet aggregation.
Thromboxane A2 powerfully stimulates platelet aggregation and secretion of platelet granules.

Extrinsic & Intrinsic Pathways (Coagulation)

Extrinsic pathway is triggered by tissue damage and involves tissue factor.
Intrinsic pathway is triggered by blood vessel damage and involves various circulating plasma clotting factors.
Both pathways converge into a common pathway, resulting in the formation of fibrin, a crucial component of the blood clot.

Fibrinolysis

Degradation and breakdown of clots via tissue plasminogen activator (tPA) and plasmin.
Involves various factors including plasminogen and plasminogen activator inhibitor-1 (PAI-1).

Therapeutic Fibrinolysis

Recombinant tissue-type plasminogen activator (rt-PA) for dissolving blood clots in myocardial infarction, stroke, and massive pulmonary embolism.

Natural Anticlotting Mechanisms

Smooth endothelial lining of vessels prevents the activation of the intrinsic pathway.
Rapid blood flow removes activated clotting factors.
Prostacyclin (PGI2) inhibits platelet aggregation and phospholipid release.
Tissue factor pathway inhibitor (TFPI) inactivates the tissue factor pathway.
Antithrombin III inhibits factors II, IX, X, XI, XII.

Fibrinolytic System

Thrombo-modulin interacts with Thrombin
Protein C and Protein S inactivate factors Va or VIIIa, thus regulating blood clotting.

Template Bleeding time

measures the time needed for a blood clot to form after a small, controlled injury—specifically a puncture wound.

Causes of Prolonged Bleeding Time

Thrombocytopenia (reduced platelet count)
Platelet function defect (e.g., aspirin)
von Willebrand disease.

Causes if Thrombocytopenia (Reduced Platelet count)

Failure of platelet production
Increased destruction of platelets
Increased consumption of platelets

Thrombocytopenia/Platelet Dysfunction Symptoms

Easy bruising
Petechiae (small, red spots) or purpura
Epistaxis (nosebleeds)
Menorrhagia (heavy menstrual bleeding)
Prolonged bleeding after minor trauma
Operative bleeding (in surgeries)

Global tests of Haemostasis

Prothrombin time (PT): Measures the time it takes for blood to clot in the presence of tissue factor (an external trigger)
Activated partial thromboplastin time (aPTT): Measures the time it takes for blood to clot in the absence of tissue factor (an internal trigger)
Thrombin time (TT): Measures the final stage of coagulation using thrombin.

Prolonged Prothrombin Time (PT) Causes

Congenital coagulation factor deficiencies
Acquired deficiencies (liver disease, warfarin therapy, vitamin K deficiency)
Other factors impacting clotting.

Haemophilia

Haemophilia is an inherited bleeding disorder characterized by the deficiency in clotting factors, resulting in prolonged clotting times.
Haemophilia A: Factor VIII deficiency; Haemophilia B: Factor IX deficiency.
Sex-linked, meaning carried on the X chromosome.
Females are carriers and usually asymptomatic.
Males are typically affected.

Haemophilia: Infantile/Childhood Symptoms

Post-circumcision bleeding
Intramuscular haematoma
Recurrent painful bleeding in joints (haemarthrosis)
Bleeding into muscles forming pseudo-tumours
Prolonged bleeding following surgeries.

Haemophilia: Adults Symptoms

Recurrent spontaneous painful bleeds in joints.
Prolonged life threatening operative bleeding and post-operative bleeding.

Haemophilia Diagnosis

Abnormal coagulation screening tests.
Prolonged aPTT.
Normal PT and TT.
Factor assays to measure deficient factors.

Haemophilia Treatment

Give the patient the missing clotting factor.
Prophylactic factor concentrates (e.g. 'normal boys')

Virchow's Triad

Endothelial injury; Abnormal blood flow; Hypercoagulability; contributing factors to thrombosis.

Risk Factors for VTE

Age; Obesity; Dehydration; Active cancer; Medical conditions; Pregnancy; Abnormal clotting; Surgery; History of VTE; HRT or birth control pills.

Kidney Function

The kidneys are responsible for filtering blood, maintaining electrolyte balance, and excreting wastes and excess substances, such as calcium and phosphate.

Body Calcium and Phosphorus Homeostasis

Calcium and phosphorus levels in the extracellular fluid are regulated by the digestive system, kidneys, and skeleton.
Kidneys are responsible for regulating phosphorus levels.
Calcium and phosphorus absorption from the gut increase with calcitriol.
Key pathways for regulating calcium homeostasis include the vitamin D pathway.

Vitamin D3

Vitamin D3 is activated by the kidneys with the 1a-hydroxylase enzyme.
Key function includes regulation of calcium.

Red Blood Cells (Erythrocytes)

Most abundant blood cells.
Biconcave discs (enhances diffusion).
Lack nuclei.
No organelles.

Erythropoiesis Factors

Erythropoietin (EPO) is a hormone that controls the production of red blood cells in the bone marrow.

Why do red blood cells suffer anaemia?

Reduced production of red blood cells and/or haemoglobin in the bone marrow
Blood loss (hemorrhage).
Reduced survival of red blood cells in the circulation.

Red Blood Cell Under Microscope

Salmon-colored
Mean cell volume (MCV)
Mean cell hemoglobin (MCH)
Central pallor

Anemia-Morphology Classification

Microcytic; Normocytic; Macrocytic

Microcytic Anaemia Causes

Defect in haem synthesis (e.g., iron deficiency)
Defect in globin synthesis (e.g., thalassemia).

Microcytic Hypochromic Aneamia

Smaller red blood cells
Low hemoglobin (low MCH)
Increased central pallor.

Macrocytic Anaemia Causes

Vitamin B12 or folic acid deficiency (nutritional or malabsorption)
Liver disease or ethanol toxicity
Some drugs interfere with DNA synthesis.

B12 Deficiency

Nutritional (vegetarians)
Gastric, such as pernicious anaemia, with anti-bodies to IF and/or GPC

Folate Deficiency

Nutritional deficiencies—in those with malabsorption in the small intestine
Excess requirement—in pregnancy

Normocytic Normochromic Anemia Causes

Recent blood loss.
Early stages of iron deficiency.
Anaemia of chronic disease
Renal failure.
Bone marrow failure.
Bone marrow infiltration (tumours).
Hypersplenism (e.g. portal cirrhosis)
Pooling of red blood cells in the spleen.

Haemolytic Anaemia

Inheretd: Abnormal red blood cell membranes; abnormal haemoglobin; defective glycolysis; defective enzyme pathways (such as pentose shunt).
Acquired: Damage to red blood cell membranes; or damage to the whole red cell.

Skeletal Muscle Tubular System

The transverse tubules (T tubules) are invaginations of the muscle cell membrane that extend into the muscle fiber. They contain extracellular fluid.
Sarcoplasmic reticulum (SR) is a network of membrane-bound structures surrounding myofibrils. It stores calcium.

Muscles

Muscles are excitable tissues with the capacity to generate and transmit electrical signals called action potentials.
Motor neurons control the contraction of several muscle fibers, and this combined system is referred to as a motor unit.

Summary of Events during Neuromuscular Transmission

Action potential in presynaptic motor axon terminals.
Increase in Ca2+ permeability. Influx of Ca2+.
Release of acetylcholine (ACh).
Diffusion of ACh to post-junctional membrane.
Combination of ACh with specific receptors on post-junctional membrane.
Increase in permeability of postsynaptic membrane to sodium.
This causes an action potential to transmit to muscles resulting in muscle contractions.

Isotonic Contraction

Muscle length changes.
Tension remains constant.

Isometric Contraction

Muscle length does not change.
Tension increases.

Muscle Fatigue

Decreased muscle strength.
Prolonged duration.
Incomplete relaxation (contracture).
Causes include metabolite accumulation, ATP depletion, decreased blood supply and impaired neuromuscular transmission.

Myasthenia Gravis

Autoimmune disease affecting neuromuscular junction
Antibodies attack acetylcholine receptors
Symptoms: Muscle weakness, often affecting the eyes, face, and limbs
Treatment: Acetylcholinesterase inhibitors
Prevent destruction of ACh
Allow more ACh to stimulate muscle contraction

A Hierarchical Model of Motor Control

Three types of movements; Reflex, rhythmic and voluntary.

Brain and Spinal Cord in Motor Control

Motor Idea → Association cortex and basal ganglia.
Motor Plan → Motor cortex—cerebellum.
Execution → Brain stem—spinal cord.

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Description

This quiz explores the concept of homeostasis, focusing on how cells maintain optimal conditions through various components including sensors, integrators, and effectors. Understand the processes that help stabilize the internal environment and how deviations are detected and corrected. Dive into the critical mechanisms that ensure our body's balance and functionality.