Circulatory and Lymphatic - Part 1

Blood and Homeostasis

• Blood is a vital liquid connective tissue responsible for transporting oxygen, carbon dioxide, nutrients, and hormones.
• It plays a role in regulating body pH, temperature, and protects against disease via phagocytosis and antibodies.
• Blood temperature averages at 38°C (100.4°F) and has a slightly alkaline pH of 7.35 to 7.45 (average 7.4).
• The color of blood changes with oxygen content: bright red when oxygenated and dark red when deoxygenated.

Physical Characteristics of Blood

• Blood is denser and more viscous than water, feeling slightly sticky.
• Interstitial fluid continuously bathes body cells and is derived from blood.

Functions of Blood

• Transportation: Carries oxygen from lungs to body cells and carbon dioxide back to lungs.
• Regulation: Utilizes chemical buffers to maintain pH balance and regulates body temperature through blood flow adjustment.
• Protection: Clots to prevent excessive blood loss and employs white blood cells for disease defense.

Formed Elements of Blood

• Red Blood Cells (RBCs/Erythrocytes): Transport oxygen and can live up to 120 days, produced in bone marrow.
• White Blood Cells (WBCs/Leukocytes): Defend against pathogens and include neutrophils, basophils, eosinophils, monocytes, and lymphocytes.
  • Lymphocytes further include B cells, T cells, and natural killer (NK) cells.
• Platelets: Cell fragments that aid in blood clotting.

Anatomy of the Heart

• The heart is approximately the size of a closed fist, located on the diaphragm near the thoracic cavity midline.
• Dimensions: Long axis about 12 cm (5 in), width 9 cm (3.5 in), depth 6 cm (2.5 in).
• Average heart mass: 250 g (8 oz) in females and 300 g (10 oz) in males.
• Positioned in the mediastinum, with two-thirds of its mass to the left of the midline.

Cardiac Function and Location

• The apex is the pointed structure formed by the left ventricle.
• Heart contractions are stimulated by the sinoatrial (SA) node, acting as the pacemaker.

Specialized Heart Tissues

• Cardiac cells exhibit excitability, allowing them to respond to stimuli and initiate action potentials autonomously.

Fetal Circulation

• Fetal circulation features unique structures for nutrient and gas exchange with maternal blood, as lungs and other organs remain non-functional before birth.
• At birth, breathing initiates a shift away from placental blood flow, leading to the closure of the ductus arteriosus and foramen ovale.

Immune System Overview

• Immunity: The body's ability to resist damage or disease, contrasting with susceptibility, which indicates vulnerability.
• Innate Immunity: Present at birth, providing immediate but nonspecific defense against pathogens without specific recognition.
  • Components include physical barriers (skin, mucous membranes) and internal defenses (natural killer cells, phagocytes, inflammation).

Hematology and Cell Functions

• Phagocytosis: The process of engulfing pathogens (cell eating).
• Pinocytosis: The process of absorbing small particles or droplets (cell drinking).
• WBC types and their primary functions:
  • Neutrophils: Fight bacterial infections.
  • Lymphocytes: Target viral infections.
  • Monocytes: Engage in phagocytosis.
  • Eosinophils: Respond to allergies.
  • Basophils: Attack parasites.

Blood Vessel Functions

• Pulmonary Arteries: Transport deoxygenated blood to lungs.
• Pulmonary Veins: Carry oxygenated blood back to the heart.
• Aorta: The largest artery, distributing oxygen-rich blood.
• Inferior Vena Cava: The largest vein, returning deoxygenated blood from the lower body.
• Capillaries: Sites of nutrient and gas exchange with the largest total cross-sectional area.