[2.3] Cardiovascular System: Blood Vessels pt. 2

Adrenal Gland

Entire organ sitting on top of each kidney with 2 distinct functional regions (cortex & medulla)

Adrenal Cortex

• Makes up the outer 80-90% of the gland.

• Secretes aldosterone

• Regulated primarily by RAAS

Adrenal Medulla

• Forms the inner core of the gland

• Secretes catecholamines (NE, E)

• Controlled by sympathetic nerves

Renin and angiotensin-converting enzyme (ACE)

Act on their substances to produce active hormone angiotensin II which raises blood pressure

2 ways in which angiotensin II raise blood pressure

1. Increase systemic vascular resistance: ↓ blood vessel radius, ↑ SVR, ↑ MAP, ↑ blood pressure

2. Stimulate secretion of aldosterone: ↑ aldosterone, ↑ reabsorption of Na⁺ ions and H₂O by the kidneys —> ↑ H₂O reabsorption, ↑ total blood volume, ↑ venous return, ↑ stroke volume, ↑ MAP,  ↑ blood pressure

Release of E and NE

Response of adrenal medulla to systemic stimulation

Effect of E and NE

Increases cardiac output by increasing the rate and force of contractions.

Antidiuretic Hormone (ADH)

Produced by the hypothalamus and released from the posterior pituitary in response to dehydration or hypovolemia (decreased blood volume)

Vasopressin

• Other name for ADH

• Causes vasoconstriction, increases blood pressure

• Promotes movement of water from the lumen to the kidney tubules into the bloodstream

Atrial Natriuretic Peptide (ANP)

Released by cells in the atria of the heart

Effect of ANP

Vasodilation

• Lowers blood pressure by promoting the loss of salt and water in urine

• Reduces blood volume

Autoregulation

• Ability of blood vessels to match blood flow to meet metabolic demands.

• Important contributor to increased blood flow through the tissue

• Controls regional blood flow in the brain: Blood distribution to various parts of the brain changes for different mental and physical activities.

Physical change stimuli

Warming → promotes vasodilation

Cooling → causes vasoconstriction

Smooth muscle in arteriole walls exhibits a myogenic response

• ↑ stretching, contracts

• ↓ stretching, relaxes

Vasodilating Substances stimuli

Vasodilating chemicals released by metabolically active tissue cells include:

• K⁺, H⁺, lactic acid, adenosine (from ATP), NO, kinins and histamine (after trauma)

Vasoconstricting Substances stimuli

Vasoconstrictors include:

• thromboxane A2, superoxide radicals, serotonin (from platelets), endothelins (from endothelial cells)

Effect of low oxygen level to pulmonary circulation

Constriction

Effect of low oxygen to systemic circulation

Dilation

Pulse

• Alternate expansion and recoil of elastic arteries after each systole of the left ventricle creates a travelling pressure wave.

• Strongest in the arteries, weaker in the arterioles, and disappears altogether in the capillaries.

Pulse rate

Number of times the arteries expand and contract in response to the heart’s activity.

Heart rate

Number of times the heart squeezes and pumps blood per minute

Temporal pulse point

Used as a pressure point to help control bleeding from a head injury.

Carotid pulse point

Frequently used in emergencies to check the pulse during CPR.

Brachial pulse point

Pulse that is checked on infants or young children receiving CPR.

Radial pulse point

Most frequently used in counting the pulse rate.

Femoral pulse point

• Must press deeply below the inguinal ligament to palpate the pulse. 

• Pulse that is checked in some burn patients with burns covering a high percentage of the body.

Popliteal pulse point

Palpated when a leg blood pressure reading is necessary (blood clot suspected in lower leg).

Dorsalis Pedis pulse point

• Good pulse rate at this site is an indicator of normal lower limb circulation.

• Mostly checked in patients with peripheral vascular problems like patients with diabetes.

Supraventricular Tachychardia (SVT)

• A type of irregular heartbeat, also called an arrhythmia. 

• A very fast heartbeat that affects the heart’s upper chambers. 

• During SVT, the heart beats about 150-220 times a minute.

Symptoms of SVT

• Very fast heartbeat

• Palpitations

• Pounding feeling in the neck

• Chest pain

• Fainting or almost fainting

• Lightheaded or dizzy 

• Shortness of breath

• Sweating

• Weakness or extreme tiredness

Causes of SVT

• Faulty signaling in the heart

• Change in electrical signals —> causes heartbeat to start early

• Heartbeat speeds up —> heart cannot fill with blood

Risk factors of SVT

• Tends to happen more in pregnant women.

• Heart diseases

• Past heart surgery

• Obstructive sleep apnea

• Thyroid disease

• Diabetes (blood sugar stays high)

• Stress

• Too much caffeine

• Too much alcohol

• Family members w/ SVT

Sphygmomanometer

Medical device used to measure blood pressue

Systolic BP

• 1st sound

• Force of blood pressure on arterial walls just after ventricular contraction

Diastolic BP

• Force exerted by the blood remaining in the arteries during ventricular relaxation

Korotkoff sounds

Sounds that are heard while taking BP

Normal blood pressure

120/80mmHg

Formula for mean arterial pressure

(SBP + 2DBP) / 3

Shock

 A failure to deliver enough O₂ and nutrients to meet cellular metabolic needs.

Effect of inadequate O₂ levels on the cells

Cells switch from aerobic to anaerobic production of ATP, and lactic acid accumulates in body fluids.

Lactic acid

• Too much lactic acid build-up in the blood due to not enough O₂

• Lowers the body’s pH level below 7.35

• Cardiac output is increasingly suppressed → organ failure → death

Hypovolemic shock

• Due to decreased blood volume

  • E.g. acute hemorrhage, 

• Inadequate intake of fluid

  • ↓ volume of body fluids, ↓ venous return, ↓ stroke volume, ↓ cardiac output.

• Replacing fluid volume as quickly as possible is essential in managing hypovolemic shock.

Cardiogenic shock

• Due to poor heart function

  • E.g. myocardial infarction, ischemia, arrhythmias

• Even with normal blood volume and cardiac output, shock may still occur if BP drops due to a decrease in systemic vascular resistance.

Vascular shock

• aka  Distributive Shock

• Due to inappropriate vasodilation

Anaphylactic shock

Allergies → ↑ histamine → causes vasodilation

Neurogenic shock

• Sudden loss of sympathetic nervous system signals

• Head trauma → malfunction of the cardiovascular center in medulla → vasodilation

Septic shock

• Severe infection

• Some bacterial toxins inflict infection → produce vasodilation

Obstructive shock

• Due to obstruction of blood flow

  • E.g. pulmonary embolism

Tension Pneumothorax Shock

Trapped air in the chest cavity → compresses the large veins and the heart → reducing blood flow back to the heart

Cardiac Tamponade Shock

Fluid buildup → ↑ pericardial pressure → compresses heart → ↓ ventricular filling → ↓ stroke volume → ↓ cardiac output

Shock compensatory mechanism: RAAS

↓ Renal blood flow → ↑ renin → RAAS → Ang II vasoconstriction + aldosterone → ↑ Na⁺/water retention → ↑ SVR & blood volume → ↑ BP

Shock compensatory mechanism: ADH

↓ BP → ↑ ADH → ↑ water reabsorption + vasoconstriction → ↑ blood volume & SVR → ↑ BP

Shock compensatory mechanism: ANS Sympathetic Activation

↓ BP → ↑ E & NE → vasoconstriction → ↑ SVR & venous return → ↑ HR and contractility → maintains BP

Shock compensatory mechanism: Release of Local Vasodilators

Hypoxia → release of vasodilators → vasodilation → ↑ local blood flow & O₂ → ↓ SVR & BP

Brachiocephalic artery

• 1st branch of the aorta

• Divides into R subclavian artery and R common carotid artery

• L common carotid and L subclavian are directly attached to the aortic arch

• R subclavian and R common carotid are connected to the brachiocephalic artery

• The brachiocephalic artery exists only on the right.

Regions supplied by Brachiocephalic artery

Head, neck, upper limb, thoracic wall

R Subclavian Artery

Gives rise to internal thoracic artery, vertebral artery (the two vertebral arteries eventually merge to form the basilar artery, which supplies blood to the brain), and axillary artery

Regions supplied by the R subclavian artery

• Thoracic wall

• Post cerebrum, cerebellum, pons, inner ear

Axillary Artery

Continuation of R subclavian artery into axilla

Regions supplied by axillary artery

Shoulder, thoracic, shoulder, scapular muscles, and humerus

Brachial Artery

• Continuation of the axillary artery

• Site of measurement of BP

• Bifurcates into radial artery and ulnar artery

Regions supplied by the Brachial artery

Muscles of arm, humerus, elbow joint

Radial Artery

Can palpate pulse as it passes thru volar aspect of forearm at the distal radial area

Regions supplied by the Radial artery

Muscles of posterior compartment of forearm.

R common carotid art

Branch of brachiocephalic art, divides into internal and external carotid art

Regions supplied by R common carotid art

Head and neck

Terminates at the temporomandibular joint, divides into superficial temporal and maxillary arteries

Int carotid art

Enters cranial cavity thru carotid foramen, giving rise to Ant. Cerebral art, Middle cerebral art, Ant. Communicating art.

Circle of Willis - Cerebral arterial circle

• Formed by int carotid art and vertebral art

• Structure that communicates with one another to make sure that the brain always has blood supply

Regions supplied by the Circle of Willis - Cerebral arterial circle

Eyeball, orbital structures, ears, nose, nasal cavity, frontal, temporal, parietal lobes of cerebrum, pituitary gland, pia mater

Pericardial art

supplies pericardium

Bronchial art

supplies bronchial tree

Esophageal art

supplies esophagus

Mediastinal art

supplies various tissues in the mediastinum

Post intercostal art

supplies skin, muscles, ribs of thoracic wall, thoracic vertebrae, meninges and spinal cord, mammary glands

Subcostal art

supplies skin, muscles, ribs. 12 thoracic vertebra, meninges, spinal cord

Sup phrenic art

supplies diaphragm muscle and pleura of diaphragm

Celiac Trunk

esophagus to duodenum + spleen, branches

L gastric art

esophagus, lesser curvature of stomach

Splenic art

gives rise to pancreatic art and L gastroomental art

Regions supplied by Splenic art

spleen, pancreas, fundus and greater curvature of stomach

Common hepatic art

gives rise to proper hepatic art, R gastric art, gastroduodenal art

Regions supplied by common hepatic art

liver, gallbladder, lesser omentum, stomach, pancreas, duodenum

Sup mesenteric art

duodenum to transverse colon

Inf pancreaticoduodenal art

pancreas and duodenum

Jejunal and ileal art

jejunum and ileum

Ileocolic art

terminal ileum, cecum, appendix, 1 st part ascending colon

R colic art

ascending colon and 1 st part transverse colon

Middle colic art

most of transverse colon

Suprarenal art

adrenal glands

Renal art

kidneys

Gonadal art

testis, epididymis, vas deferens, ovaries, uterine tubes, in both male and female - ureter,

Common iliac art

pelvic muscle wall, pelvic organs, external genitals, lower limbs, gives rise to int and ext iliac art

Int iliac art

external genitalia, pelvic muscles, pelvic organs, medial thigh muscles

Ext iliac art

lower abdominal wall, cremasteric muscles (males), round ligament of uterus (females)

Femoral art

supplies thigh muscles, femur, ligaments of tendons around knee joint

Superior Vena Cava (SVC)

Drains regions above the diaphragm (head, neck, upper limbs, thorax)

Inferior Vena Cava (IVC)

Drains regions below the diaphragm (abdomen, pelvis, lower limbs)

Coronary Sinus

Drains blood from the myocardium of the heart

Internal Jugular Vein

Drains regions above the diaphragm (head, neck, upper limbs, thorax)

Path of Internal Jugular Vein

Begins at jugular foramen as  continuation of sigmoid sinus, descends through the neck with internal carotid artery and vagus nerve in carotid sheath, joins the subclavian vein to form the brachiocephalic vein