Chapter 19

Blood vessels are responsible for transporting blood throughout the body from the heart.
Blood is pumped out of the heart into the aorta, which begins systemic circulation.
Major arterial branches of the aorta include:
- Brachiocephalic artery
- Left common carotid artery
- Left subclavian artery

Blood travels from the aorta to smaller arteries, eventually branching into arterioles.
Capillaries:
- Site of gas exchange between blood and tissues.
- Oxygen is delivered to tissues, while carbon dioxide is collected from them.
- Blood circulation involves oxygenated blood delivered to tissues and deoxygenated blood returning to the heart.

Arteries:
- Carry blood away from the heart.
- Major arteries branch into smaller ones, leading to arterioles and capillaries.
Veins:
- Carry blood back to the heart, with major veins including:
  - Superior vena cava
  - Inferior vena cava
- Blood returns from capillaries to venules and then into larger veins.

Capillaries are the smallest blood vessels, enabling exchange of oxygen and carbon dioxide.
Oxygenated blood moves into tissues; carbon dioxide is transferred back into the bloodstream for removal.

Study of:
- Blood pressure effectiveness in arteries vs capillaries
- Regulation of blood pressure (short term vs long term)
- Renal mechanisms affecting blood flow.

Lymphatic vessels drain lymphatic fluid and filter it through lymph nodes and spleens, integrating into blood circulation.

Walls of Blood Vessels:
- Consist of three layers:
  - Tunica intima: Inner layer of squamous epithelium.
  - Tunica media: Middle layer with smooth muscle; thicker in arteries than veins.
  - Tunica externa: Outer layer containing connective tissue.
Larger veins have more elastic fibers, adapting for stretch and carrying capacity.

Blood pressure readings fluctuate with heart contractions:
- Systolic pressure: Highest when heart contracts.
- Diastolic pressure: Lowest when heart relaxes.
Major pressure drop occurs in arterioles, prior to capillary beds.

Increase in arterial pressure due to:
- Increased stroke volume and heart rate.
- Increased blood vessel length and viscosity.
- Decreased diameter of blood vessels.
Baroreceptor reflex helps maintain blood pressure homeostasis:
- Located in the aortic arch and carotid arteries.
- Modulates sympathetic and parasympathetic responses based on blood pressure changes.

Hormones Influencing Blood Pressure:
- Epinephrine and norepinephrine: Increase cardiac output and total peripheral resistance.
- Angiotensin II: Increases resistance in blood flow.
- Antidiuretic hormone (ADH): Promotes water retention and affects blood volume.
- Atrial natriuretic peptide (ANP): Decreases blood volume and induced vasodilation.
- Renin-angiotensin-aldosterone system: Regulates blood pressure and fluid balance.