Human Physiology Midterm 1

Chap 11-13

What are the four main components of blood?

Plasma, erythrocytes, leukocytes, platelets

Which component makes up the largest percentage of blood volume?

Plasma (~55%)

Which formed element is most abundant?

Erythrocytes (RBCs)

Rank formed elements from most to least numerous.

Erythrocytes > platelets > leukocytes

What is plasma composed of?

Water, plasma proteins, nutrients, gases, wastes, hormones

Describe the appearance of centrifuged blood.

→ Top: plasma
→ Middle: buffy coat
→ Bottom: erythrocytes

What makes up the buffy coat?

Leukocytes and platelets

Why do erythrocytes settle at the bottom of a centrifuged blood sample?

They are the densest and most numerous cells

What are the three major plasma proteins?

Albumin, globulins, fibrinogen

What is the primary function of albumin?

Maintains osmotic pressure

Why is albumin important for blood volume?

Prevents excessive fluid loss from capillaries

What is the general function of globulins?

Transport and immune defense

Which subclass of globulins function as antibodies?

Gamma globulins

What is fibrinogen’s role in the blood?

Blood clot formation

Describe the functions of the major plasma proteins.

→ Albumin: osmotic pressure
→ Globulins: transport, immunity
→ Fibrinogen: clotting

Describe the shape of erythrocytes.

Biconcave discs

Why is the biconcave shape important?

Increases surface area for gas exchange

Which organelles are absent in mature erythrocytes?

Nucleus, mitochondria, ribosomes

Why do erythrocytes lack mitochondria?

They do not consume the oxygen they transport

Define haemoglobin.

Iron-containing protein in RBCs that binds oxygen

Describe the structure of haemoglobin.

Four globin chains with iron-containing heme groups

What molecule binds directly to oxygen in haemoglobin?

Iron (Fe²⁺) in heme

List three functions of haemoglobin.

→ Oxygen transport
→ Carbon dioxide transport
→ Blood pH buffering

What is erythropoiesis?

Production of red blood cells

Where does erythropoiesis occur?

Red bone marrow

Which hormone regulates erythropoiesis?

Erythropoietin (EPO)

What stimulates the release of erythropoietin?

Low blood oxygen levels

What determines ABO blood type?

Presence or absence of A and B antigens on RBCs

What antibodies are present in Type O blood?

Anti-A and anti-B antibodies

Which blood type is the universal donor?

O negative

Which blood type is the universal recipient?

AB positive

What is the Rh factor?

Presence (+) or absence (−) of the D antigen

Why is Rh incompatibility dangerous during pregnancy?

Maternal antibodies can destroy fetal RBCs

Define anaemia.

Reduced oxygen-carrying capacity of blood

List two causes of anaemia.

→ Low RBC count
→ Low haemoglobin

What is primary polycythaemia?

→ Excessive RBC production due to bone marrow disorder

What causes secondary polycythaemia?

→ Chronic hypoxia (e.g. high altitude, lung disease)

How do leukocytes differ from erythrocytes?

Have nuclei, involved in immunity

What is the role of neutrophils?

Phagocytize bacteria

What is the role of eosinophils?

Defend against parasites, allergic reactions

What is the role of basophils?

Release histamine, inflammation

What is the role of monocytes?

Become macrophages in tissues

What is the role of lymphocytes?

Adaptive immunity

What are the two main types of lymphocytes?

B cells and T cells

What is antibody-mediated immunity?

Immunity via antibodies produced by B cells

What is cell-mediated immunity?

Immunity via T cells destroying infected cells

What are platelets derived from?

Fragments of megakaryocytes

What is the function of platelets?

Blood clotting

Define haemostasis.

Prevention of blood loss

List the three steps of haemostasis.

→ Vascular spasm
→ Platelet plug formation
→ Coagulation

What triggers the clotting process?

Tissue injury / exposed collagen

What is the role of thrombin?

Converts fibrinogen to fibrin

What forms the meshwork of a clot?

Fibrin

Which factor initiates the intrinsic pathway?

Factor XII

What is the main difference between intrinsic and extrinsic pathways?

Intrinsic starts inside blood; extrinsic starts with tissue damage

What is clot retraction?

Platelets contract to stabilize the clot

What enzyme dissolves clots?

Plasmin

Define immunity.

The body’s ability to resist and eliminate disease-causing organisms

List the main responsibilities of the immune system.

→ Prevent infection
→ Limit spread of pathogens
→ Destroy infected or abnormal cells

Key difference between bacteria and viruses?

Bacteria are living cells; viruses require host cells to replicate

Define virulence.

The degree of pathogenicity of a microorganism

List the main layers of the skin.

Epidermis, dermis, hypodermis

Why is the epidermis effective as a defence barrier?

Keratinized cells form a tough, waterproof barrier

Which skin cells provide immune surveillance?

Langerhans cells

Function of melanocytes in immunity (indirect)?

Protect against UV damage that can compromise skin integrity

Name key antimicrobial skin secretions.

Sebum, sweat

How does the respiratory tract defend against pathogens?

Mucus traps particles; cilia move them out

How does the genitourinary tract reduce infection risk?

Urine flow flushes microbes; acidic environments inhibit growth

Differentiate innate and adaptive immunity.

→ Innate: fast, non-specific
→ Adaptive: slow, specific, memory-based

What are plasma cells?

Differentiated B cells that secrete antibodies

Name three major lymphoid tissues and their functions.

→ Bone marrow: blood cell production
→ Thymus: T cell maturation
→ Lymph nodes: immune activation

Purpose of inflammation?

Localize, eliminate pathogens, and promote tissue repair

List the main steps of inflammation.

→ Vasodilation
→ Increased permeability
→ Leukocyte emigration
→ Phagocytosis

Define vasodilation.

Widening of blood vessels to increase blood flow

What is leukocyte emigration (diapedesis)?

Movement of leukocytes from blood into tissues

What are opsonins and their function?

Molecules that enhance phagocytosis by coating pathogens

Role of interferon in body defence?

Role of interferon in body defence?

How do phagocytes amplify inflammation?

Release cytokines and chemotactic chemicals

How does the complement system kill microbes directly?

Forms membrane attack complex (MAC) that causes lysis

Basic structure of an antibody?

Two heavy chains, two light chains, variable and constant regions

Which antibody region binds antigen?

Fab region

Define natural killer (NK) cells.

Innate lymphocytes that kill virus-infected and cancer cells

Define clonal selection.

Activation and replication of lymphocytes specific to an antigen

Function of helper T cells (CD4⁺)?

Coordinate immune responses via cytokines

Function of cytotoxic T cells (CD8⁺)?

Kill infected or cancerous cells

Function of regulatory T cells?

Suppress immune responses, prevent autoimmunity

Why are memory cells important?

Enable faster, stronger secondary immune responses

Differentiate immunodeficiency vs inappropriate immune attack.

→ Immunodeficiency: weak response
→ Inappropriate attack: excessive/misdirected response

Define anaphylactic shock.

→ Severe systemic allergic reaction causing widespread vasodilation and drop in blood pressure

List the structures of the respiratory system in order.

→ Nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli

What is the primary muscle of inspiration?

→ Diaphragm

Which muscles assist with forced inspiration?

→ External intercostals, sternocleidomastoid, scalenes

Is quiet expiration active or passive?

→ Passive (elastic recoil)

Which muscles are used during forced expiration?

→ Internal intercostals and abdominal muscles

What forces cause the lungs to want to collapse?

→ Elastic recoil and surface tension

What prevents alveoli from collapsing?

→ Pulmonary surfactant

What happens during quiet inspiration?

→ Diaphragm contracts → thoracic volume ↑ → alveolar pressure ↓ → air flows in

What happens during quiet expiration?

→ Diaphragm relaxes → elastic recoil pushes air out

Why is a pressure gradient essential for breathing?

→ Air flows from high pressure to low pressure

How does barometric pressure affect respiration?

→ Lower barometric pressure reduces oxygen availability