Cardiovascular System in Vertebrates

Circulatory System

• Functions: Transports gases between external and internal respiration.
• Also transports: products of digestion, hormones, waste products, cells and chemicals of the immune system, heat.

Two Vascular Systems

• 1. Cardiovascular system: blood, vessels, heart.
• 2. Lymphatic system: lymphatic vessels and lymph.

The Lymphatic System

• Lymphatic vessels and lymph
• Cervical lymph nodes
• Lymphatics of the mammary gland
• Cisterna chyli
• Thoracic duct
• Thymus
• Axillary lymph nodes
• Spleen
• Lumbar lymph nodes
• Lymphatics of the upper limb
• Pelvic lymph nodes
• Lymphatics of the lower limb
• Inguinal lymph nodes

Formed Elements of Blood

• Blood: Plasma - fluid component
• Cells:
  • Erythrocytes (red blood cells): carry hemoglobin.
  • Leukocytes (white blood cells): immune response.
  • Thrombocytes (platelets): important for clot formation.
• Plasma: 95% water, proteins, glucose, clotting agents, electrolytes.

Cardiovascular System

• Do all vertebrates have red blood cells and hemoglobin?: No.

  • 16 species of crocodile icefish occur in the Antarctic (Channichthyidae)
  • Have neither red blood cells nor hemoglobin.
  • No myoglobin in skeletal muscles.
  • O2 transported in plasma
  • Can live in waters down to 28°F with antifreeze proteins.
  • Scale-less, no swim bladders.
  • Low-density bone.
  • Low metabolism.

• Q: Does the blood passing through a shark heart differ from that passing through a dog's (or pigeon's) heart?: Yes!

  • Shark - all low-O2 blood, one stream
  • Dog - 2 streams, one low-O2 other high-O2

Vessels

• Arteries: take blood away from heart.

• Veins: bring blood back to heart

• Is it that arteries always carry oxygenated blood?: No.

  • Pulmonary arteries (mammals): blood to lungs, low O2.
  • Ventral aorta (shark): blood to gills, low O2.

• Highest blood pressures

• Walls with high elastin fiber content (T. intima & media).

• Absorbs sudden surge of energy (pulse), stretches.

• Elastic recoil moves blood along more smoothly.

• Arteriosclerosis (hardening of arteries)

Microcirculation

• Arterioles - capillary beds - venules

• Arterioles & Venules: Smooth muscle + a little elastin.

• Capillaries: site of exchange, thin walls with epithelium only & narrow lumen, facilitates transport of gases, nutrients, waste, water, ions, heat.

• Precapillary sphincters: regulate flow to capillary beds, adjust to activity levels, under nervous + hormonal control.

• Capillary Beds: overlap, redundancy, tissues with multiple beds, with sphincters, adjust blood flow to activity level.

• Blood to active tissues (e.g., Thanksgiving "food coma," running w/o digesting - ischemia).

• Heat transfer (cooling - blood to skin, ectotherm – adjusting to behavior for warming/cooling).

Veins

• Large volume
• Thinner walls, smooth muscle, little elasticity, 'baggy'.
• Reserve volume
• Up to 70% of blood may be in veins at one time
• With activity, vasoconstriction, more blood in arterial vessels.
• Blood flow: one-way valves prevent backflow, skeletal muscle activity forces blood thru system, activity moves more blood from reserve into arterial vessels.

Cardiovascular System

• With long necks:
  • Cardiovascular system must adjust with head movements to maintain consistent flow/pressure.
  • Aortic pressure adjusts with head movements.
  • Pooling prevented likely by vasoconstriction (raised) and vasodilation (lowered).
  • Also affects kidneys.
  • Arterial flow in legs very high.
  • Lots of connective tissue surrounds leg vessels to prevent pooling.

Circulation Systems

• Single Circulation
• Blood passes through heart once during complete circuit
• e.g. Shark, Perch (fish)
• Double Circulation
• Blood passes through heart twice during complete circuit
• e.g. Pigeon, you. (birds, mammals).

Blood Vessels

• From mesoderm.
• Form early on, e.g., 48 hours in chick, quickly become large, complex.

Arterial Vessels

• Follow similar embryonic pathways in all vertebrates.
• Diverge through late stages of development.
• Basic pattern:
  • Single ventral aorta from heart
  • Six pairs of branchial arteries.
  • Paired dorsal aortae
• Each arch with afferent & efferent branchial arteries.
• Basic pattern: all embryos, ~ shark, most fish.

Functions of Basic Pattern

• Delivering low-O2 blood to gills.
• Each arch with afferent & efferent branchial arteries.
• Deliver blood to brain and head, internal & external carotids.
• Usually branch off anterior most arch (I).
• Internal carotids from afferent branchial or dorsal aortae.

Example: Lamprey

• Pattern close to basic ideal.
• 8 pairs of arches
• External carotids from efferent branchial III.

Example: Shark

• Pattern close to basic ideal
• Not a full set of arches.

Venous System

• Very variable in arrangement (even within species).
• Functions
  • Drain body tissues (systemic, jugular).
  • Drain lungs - pulmonary veins.
  • Extension from lungs.
  • Hepatic Portal System
  • Renal Portal System

Venous System: Vitelline Veins

• Among first to form in embryo.
• Drain from yolk, along gut and into heart.
• Bring nutrients from yolk.
• Bring O2-rich blood in amniotes.
• Gets incorporated into liver & hepatic portal system.

Venous System: Main Vessels

• Primitively: paired anterior cardinal veins, paired posterior cardinal veins, paired common cardinal veins
• Derived: single precava (cranial vena cava) & postcava (caudal vena cava).

Renal Portal System

• In all vertebrates except mammals
• Connects caudal blood (from tail) to kidney via renal portal vein
• Subcardinal or renal vein drains kidneys
• Blood then processed by kidney
• Two factors likely favored this:
  • Primitively: tail/axial muscles biggest and most active
  • Low pressure of venous blood suitable for recovery of H2O and solutes.

Heart

• Hagfish: unusual in having accessory -like structures, initially, simple tubular structure with four chambers in a row.
• Heart beat: contraction intrinsic to cardiac muscle, intercalated disks connect cells and ensure coordination of contraction.
• Heart beat rate: under nervous & hormonal control, contraction strength proportional to volume of returning blood.
• Heart of 'fish': undivided = single circulation, 4 chambers in S-shaped arrangement: sinus venosus, atrium, ventricle, conus arteriosus (or bulbus arteriosus).

Heart of "Fish"

• Operation
  • Venous blood: muscular activity around veins drives blood toward heart. Aspiration effect.
  • Sequential contractions move blood from one chamber to the next. Vales (SA, AV, conal or bulbar) prevent backflow.

Heart Trivia

• The entirety of your blood passes through your heart in one minute
• Heart could empty a swimming pool in a week.
• Heart was the last organ to be operated on (largely due to challenges of working on a very active organ).

Heart of Reptiles

• Complex and plumbing (3 aortae).
• Accommodates apnea, periods of non-breathing.
• Occurs when submerged, hibernating/aestivating/quiet time.
• Single ventricle but partially divided with shunt
• Muscular ridge separates cavum venosum (r) from cavum pulmonale (I)
• Cavity arteriosum (interventricular canal) to cavum venosum
• Fills with high-O2 blood from left atrium when breathing.
• Separation of O2-poor from O2-rich blood
• Accommodates apnea
• Can tune volume of blood to lung independent from that to body/head

Heart of Crocodilians

• Ventricles fully divided
• Has foramen of Panizza
• Connects left and right systemic arches
• Shunts high-O2 blood when breathing to body
• Limited use during apnea.

Hearts of Birds and Mammals

• More straight forward, 2 atria, 2 ventricles
• Cannot vary. Blood to lungs (volume) always equals blood to body (volume)
• Apnea in diving birds and mammals, decrease in rate (bradycardia), anaerobic metabolism in muscles increases, microcirculation alters blood flow to needed organs/tissues.

Major Shift in Circulation at Birth for Placental Mammals

• Transition involves a few key features of embryo-neonate
• Embryo: Umbilical vein, ductus venosus, foramen ovale, ductus arteriosus, umbilical arteries
• Neonate: Round ligament of liver, fossa ovalis, ligamentum arteriosum, round ligament of urinary bladder

Patent Foramen Ovale (PFO)

• In 25-33% of adults foramen ovale never closes
• Pressure largely keeps closed, but some leakage.
• Increased risk associated with stroke, migraines, decompression illness, high-altitude pulmonary edema.

Heat Transfer

• Microcirculation moves blood to or away from skin
• Retes (Adjacent networks of arteries and veins that act as heat blocks with countercurrent flow)
  • Importance in aquatic vertebrates (e.g., duck feet, dolphin fins)
  • Sperm production - pampiniform plexus, countercurrent heat exchange
• Carotid rete: Keeps brain from overheating, cools blood returning from nose/turbinates by passing blood along carotids

This quiz explores the intricate details of the cardiovascular system in vertebrates, focusing on the roles of afferent and efferent branchial arteries. It also examines the evolutionary aspects and developmental patterns of blood vessels across different vertebrate groups, including lampreys and lungfish.