Respiration and Gas Exchange

• Body pH is homeostatically regulated through respiratory compensation for metabolic alkalosis/acidosis.
• ACE hormone secretion is a function of breathing.
• Air flows from areas of high pressure to areas of low pressure.
• Resistance to airflow depends on the diameter of the tubes through which air flows.
• External respiration facilitates the exchange of O2 and CO2 between the lungs and blood and transports O2 and CO2 by blood.
• Internal respiration is the exchange of gases between blood and cells.
• Pulmonary Circulation: Capillaries increase the diffusion rate via thin simple squamous cells.

Types of Respiration

• Ventilation: Movement of gases from inside to outside.
• Gas exchange: From tissue to the circulatory system.
• Cellular respiration: Generates large yield of ATP.

Pleural Sacs

• Visceral and parietal pleural sacs enclose the lungs within the thoracic/pleural cavity
• Serous fluid is located between the membranes
• Serous Fluid lowers friction between membranes and holds lungs tight against thoracic wall.
• Pleuritis: Inflammation of the pleura which creates respiratory issues.

Upper Respiratory System

• Pharynx (non-keratinized stratified squamous)
  • Pharyngitis: ex. Sore throat
• Epiglottis: Elastic cartilage
• Vocal Cords vibrate within the larynx
• Nasal Cavity: Regulates temperature, humidification, and filtration.
  • Nasal Plasticity: Gradual change to adapt mouth breathing.
• Esophagus is posterior to the trachea
• Tongue enables speech and swallowing
• Larynx contains the vocal cords

Lower Respiratory System

• Trachea (hyaline cartilage/no fibers + pseudostratified ciliated columnar)
• The lungs include the right and left lungs, as well as the right and left bronchus (pseudostratified ciliated columnar)
• Bronchioles (pseudostratified ciliated columnar)
• Diaphragm enables respiration.
• Goblet Cells/Mucosal: secrete mucus (mucin is a glycoprotein)
• Fissures: separate lobes of the lungs

Alveoli

• Primary site of gas exchange, consisting of simple squamous cells.
• Type 1 cells make up alveolar air sacs allowing gas exchange.
• Type 2 releases surfactant which decreases surface tension, and prevents hydrogen bonds from binding because it is polar and non-polar.
• Type 3 are also known as macrophages (immune cells).
• The flow of blood in the lungs: Right ventricle → Pulmonary Trunk → Pulmonary Arteries → Lung → Pulmonary Vein → Left Atrium

Bronchi

• Primary
• Secondary
• Tertiary
• The trachea transitions to bronchi and then to bronchioles and loses hyaline cartilage to increase permeability to alveoli and increase diffusing capacity.
• Atmospheric Pressure: 760 mmHg (1 ATM) (at sea level)

Gas Laws

• Dalton’s law: Total atmospheric pressure equals sum of all partial pressures (O2, CO2, water vapor, methane, nitrogen) where nitrogen has the highest concentration in the atmosphere
• Boyle’s law: describes pressure-volume relationships where pressure is inversely proportional to volume -- As volume increases, pressure decreases. -- As volume decreases, pressure increases.

Lung Volumes

• Tidal Volume (VT): volume of air during 1 inhalation or exhalation (quiet breathing)
• Inspiratory Reserve Volume (IRV): additional volume above tidal volume (forced breathing)
• Expiratory Reserve Volume (ERV): forcefully exhaled after the end of a normal expiration (forced breathing)
• Residual Volume (RV): volume of air in the respiratory system after maximal exhalation

Lung Capacity

• Vital capacity (VC) = IRV + ERV + tidal volume
• Total lung capacity (TLC) = Tidal volume+ IRV + ERV + residual volume
• Inspiratory capacity = TV + IRV
• Functional residual capacity = ERV + RV
• The Phrenic Nerve regulates the diaphragm through contracting/relaxing. -- If inflamed = hiccups

Diaphragm Contraction/Relaxation

• A. Diaphragm contracts ribcage elevates
• B. Inspiration: Gas comes from outside → in / Thoracic volumes increases & diaphragm contracts/flattens
• C. Expiration: Diaphragm relaxes volume decreases/ pressure increase

Intrapleural Pressure

• Usually negative.
• Pneumothorax (if punctured, gas flows inside = collapsing/ (no negative pressure) -- Treatment: one-way valve.
• Hemothorax (blood in lung = collapsing).
• Inspiration: pressure drops.
• Expiration: pressure return to normal value.

Ventilation Types & Patterns

• Hyperpnea: Rapid breathing (metabolic demand) during exercise.
• Hyperventilation: Rapid breathing (non-metabolic demand) and possible for emotional hyperventilation
• Hypoventilation: Shallow breathing in Asthma
• Tachypnea: Fast breathing like panting.
• Dyspnea: Difficulty breathing for Pathologies.
• Apnea: Complete cessation of breathing like Voluntary breath holding (sleep apnea).
• Obstructive Lung Disease: can inspire easily but hard to expire (increased compliance/low elastins). -- ex: Sleep apnea, COPD, epidema, chronic bronchitis -- Leads to Respiratory acidosis, and it is compensated metabolically through increased bicarbonate reabsorption.
• Restrictive Lung Disease: can expire easily but hard to inspire (increased elastin/low compliance buildup of CO2). -- pulmonary fibrosis. -- Problem with recoil tendencies (exhaling easily) elastins. --Leads to Respiratory Acidosis
• Forced Vital Capacity: forced expiratory Volume in 1 sec. -- It differentiates lung physiology of being strengthened or non-strengthened.
• Gas Exchange: Occurs in alveoli (O2 goes in blood/ CO2 goes out the blood), Capillaries, Tissues (O2 comes out of blood/ CO2 goes into blood).
• Regulated Variables: O2, CO2, and pH.
• During Hypoxia: too LITTLE O2 = HIGH CO2
• During Hypercapnia: build up of CO2 = more acidic
• Alveoli/Blood: PO2 alveolar air > PO2 blood and PCO2 blood > PCO2 alveolar air
• Blood/Tissues: Oxygen in blood is higher than tissue and PO2 blood > PO2 tissue with PCO2 tissue > PCO2 blood -- Deoxygenated Blood: 40 mm Hg -- Oxygenated Blood: 100 mm Hg

During Expiration

• P (in) is greater than P (out) which leads to a decrease in PN, Diaphragm, Vt, and an increase in Pt

During Inspiration

• P(out) is greater than P (in) which leads to an increase in PN, Diaphragm, Volume, and a decrease in Pt

Low Alveolar PO2

• Decreases O2 uptake
• Occurs if inspired air has abnormally low oxygen Content
• Higher altitude decreases PO2

Alveolar Ventilation

• Low alveolar PO2 if alveolar ventilation is inadequate -- (hypoventilation)
• Decreased lung compliance (asbestosis)
• Increased airway resistance (COPD)
• CNS depression: alcohol poisoning, drug overdose (affects respiratory center in the brainstem)
• High Compliance = difficulty expiration (build up of CO2)
• High Elastins = difficulty inspiration (pulmonary fibrosis)
• A barrier of cells form between lung and blood which can prevent gas exchange.
• O2 from alveoli moves from the barrier to plasma, binding to hemoglobin for O2 transport, while, CO2 diffuses from plasma to alveoli to be expelled
• Hypoxia can occur if the body lack enough oxygen.

Emphysema:

• Destruction of alveoli reduces surfaces area for gas exchange which leads to less oxygen being absorbed into bloodstream

Fibrotic Lung Disease:

• Thickened Alveolar membrane which slows diffusion of gases, high elastins loss of lung compliance which causes ventilation difficulty and reduced oxygen uptake.

Pulmonary Edema:

• Fluid accumulates in interstitial space in lungs which increases the distance where gas must diffuse and causes oxygen transfer insufficient and decreases diffusion.

Asthma:

• Increased airway resistance due to bronchoconstriction that reduces airflow into alveoli, makes it difficult for O2 to enter and CO2 to exit which leads to low oxygen levels in blood and needs adrenergic receptors

Oxygen transport in blood

• When O2 enters capillaries, it first dissolves in plasma and then Oxygen binds to hemoglobin. -- Hb + O2 ↔ HbO2 (oxyhemoglobin)- reversible reaction allowing O2 to be released when needed -- 4 hemes = 4 O2 binding-sites
• Oxygen binding obeys the law of mass action: -- ↑PO2 shifts reaction to R (Hb + O2 → HbO2)- IN LUNGS (more oxygen) --↓PO2 shifts reaction to L (Hb + O2 ← HbO2)- AT TISSUE (less oxygen)
• The reaction ensures RBCs become saturated with O2 before traveling through the bloodstream.

Carbon Dioxide Transport

• CO2 transport in blood (bicarbonate ion – HCO3) maintains acid-base balance and ensures removal of metabolic waste via diffusion or when it binds to hemoglobin to make carboxyhemoglobin or it is turned into bicarbonate
• Bicarbonate rxn: transported in bloodstream, it reacts w/ water and RBC = carbonic acid → high concentration of carbonic anhydrase -- Maintains homeostasis and pH levels --1 Bicarbonate OUT = 1 Chlorine IN (chloride shift for tissue) --1 Chloride OUT - 1 Bicarbonate IN (chloride shift in alveoli)
• It is difficult to dissolve because it is not polar.
• Bicarbonate = non-metal to non-metal (covalent bond) --Visceral sensory command: ex. BP (baroreceptors found in aortic arch/carotid arteries) --Medulla Oblongata (primary regulator of all visceral commands) & Pons: activates Phrenic Nerve Dorsal respiratory group (DRG):
• The muscles of inspiration receive input from VRG.
• Then signals are sent to the Phrenic nerve to the diaphragm from the pons & medulla for contraction
• Intercostal nerves carry signals to intercostal muscles and then receive sensory input from central and peripheral chemoreceptors that monitor blood CO2 and, to a lesser extent O2

Respiratory Groups

• Pontine respiratory group: helps refine breathing patterns & output to the medulla to ensure smooth respiratory rhythm
• Ventral respiratory group (VRG):
• One region = pre-Bötzinger complex: basic pacemaker activity (generates rhythms that control breathing)
• Other regions control muscles involved for active expiration or deeper forceful inspiration (labored breathing)
• Innervate muscles of the larynx, pharynx, and tongue to keep upper airways open during breathing
• Peripheral chemoreceptors are in the carotid bodies (carotid arteries) and sense changes in PO2, pH, and PCO2. --↓PO2, pH, and ↑PCO2 initiate increase in ventilation
• O2 must fall below 60 mm Hg to trigger reflex.
• Central chemoreceptors are in the CNS (ventral surface of medulla) and respond to changes in PCO2 in the CSF. --Arterial ↑PCO2, diffuses into CSF -- CO2 is converted to bicarbonate and H+ which stimulates chemoreceptors to adjust ventilation
• Digestive System
• The Gastrointestinal system and Alimentary Canal has 2 components. The Oral cavity and the Gastrointestinal tract. -- Oral cavity: digestion begins here. Mouth and Pharynx
• Gastrointestinal tract: GI tract

Anatomy of the Digestive Tract Cont.

• Food travels through esophagus, stomach, small intestine, and then large intestine.
• The gut includes the stomach through the anus.
• This is primarily involved in digestion (chemical and mechanical).
• Tract is divided by sphincters (muscular one-way valves both voluntary/involuntary)
• Accessory glandular organs secrete materials that aid in digestion like the Salivary glands, pancreas, and liver.
• Chyme (semi-liquid) is essential for breakdown of food and absorption of nutrients

Products of Digestion

• Nutrients cross epithelium into interstitial fluid and then they enter through interstitial fluid to blood or lymph to be distributed
• Waste is excreted from the GI tract from the anus.
• Digestive system is continuously exposed to external environment and is home to commensal microorganisms

Salivary Glands

• Salivary Secretion is autonomic control (involuntary)
• They contain digestive enzymes like amylase (pytalin) to start breakdown of carbohydrates to prepare food for digestion.
• 3 Types of glands (glossopharyngeal nerve): -- Parotid (by cheeks) – watery solution of enzymes (amylase) -- Submandibular (lower jaw) – mixed water + saliva -- Sublingual (under tongue) – mucus w/ saliva
• Esophagus move food through coordinated contractions known as peristalsis

Stomach

• Fundus → body → antrum (gastric juices mixed w/ food) hydrochloric acid and digestive enzymes → chyme: a semi-liquid substance
• Immunity | Storage | Digestion are the Functions of the stomach
• The Inner surface of the stomach contains rugae/folds that allows it to expand & accommodate food
• This system has it own network called the Myenteric plexus that coordinates digestion
• Pylorus: controlled by pyloric valve that regulates passage of partially digestive food to the small intestine
• Small intestine is made up of the duodenum, jejunum and ileum.
• Digestive enzymes from the pancreas and bile from the liver aid in digestion of fats, proteins, & carbohydrates
• It is known as the primary site of nutrient absorption.
• The inner surface is lined with circular folds that contain villi (maximizes nutrient absorption), crypts (specialized cells helping in cell secretion and renewal), and lacteal (absorbs fats in lymphatic capillary)
• Large intestine help water is reabsorbed and beneficial bacterias process left-over food -- Composed of the colon → rectum → anus with external anal sphincter that expels food and waste

Digestive Wall

• GI Tract wall has 4 layers
• 1. Mucosa (forms inner lining of GI tract/ mainly epithelial tissue)
  • 3 Sublayers: --- Mucosal Epithelium: secretion of digestive enzymes & mucus and provides protective barrier --- Lamina Propria (CT): contains immune components which include Peyer’s patches (defend against pathogens/gut-associated lymphoid tissues GALT)
  • Muscularis Mucosae: consists of thin-smooth muscle fibers aiding in movement of food/secretion
• 2. Submucosa is the middle layer made of CT that provides structural support/elasticity & contains submucosal plexus of enteric nervous system that regulates glandular secretions and bloodflow
• 3. Muscularis Externa is the outer wall/ composition of smooth muscle and is composed of 2 layers of smooth muscle that coordinates rhythmic contractions like peristalsis and contains myenteric plexus of enteric nervous system (GI tracts’ own neural network)
• 4. Serosa is the outer covering of GI tract and a continuation of peritoneal membrane that forms protective sheets of mesentery that helps anchor digestive organs in place allowing movement and reducing friction

Basic Processes of Digestion

• Digestion: breakdown of food through mechanical digestion (chewing/muscular contraction) and chemical digestion (enzymes/acids breaking down complex molecules)
• Absorption: primarily in small intestine, from GI lumen to ECF where nutrients are transported (carbohydrates, proteins, fats, vitamins & minerals) and pass through intestinal lining to bloodstream or lymphatic system
• Secretion: release of digestive enzymes, hormones, and mucus from cells into lumen or ECF. Organs involved: salivary glands, stomach, pancreas, and the intestine produce secretions
• Motility: movement of food and waste through GI tract = muscle contraction (segmentation - mixes content to enhance digestion & absorption/peristalsis- propels food forward)

Motility

• Allows move food continuously.
• Mechanically mix food to break into small particles
• Tonic Contraction: help maintain muscle tone & regulate food passage (min or hrs)
• Phasic Contractions: mixes and propels food (seconds)
• Interstitial Cells of Cajal generate electrical impulses to regulate contraction patterns of GI tract
• Migrating Motor Complex enables bulk flow

Regulation

• Peristalsis contraction over contraction happens in the esophagus
• Segmental Contraction causes mixing movement in one direction in the small and large intestine
• Neurotransmitter during Peristalsis: Acetylcholine
• Enteric Nervous System/Parasympathetic enables both short reflex/2nd brain via: --Controls motility --Secretion --Growth --- Allows Intrinsic neurons/extrinsic neurons ---Maintains diffusion barrier ---Functions as an Integrating center to process sensory information
• Central Nervous System (long reflex) -- Cephalic reflex (anticipatory response)

Cephalic Phase

• Anticipation & stimulation to prime GI tract
• Create specialized reflex anticipatory response and secretion of gastric acids/enzymes through: --Chemical (starch)/mechanical (mastication) digestion --Defense --Taste --Soften & lubricate food
• Stimulates: Inhibits somatostatin to allow acid production and Parietal cells secrete HCl in addtion to Secretion of pepsinogen
• Activating muscle in pharynx to push food down (swallowing), which is controlled by the medulla (Deglutition)
• Functions of the Gastric phase: provides immunity, Storage and Digestion , defense and promotes histamine to stimulate acid secretion that functions as a Positive Feedback
• During the Cephalic Phase, gastrin secretes hydrochloric acid and Somatostatin inhibits parietal cells

Gastrin Secretion

• Gastrin is released by G cells which leads to HCl production by parietal cells Acid Secretion happens when the Parietal cells secrete gastric acid (HCI)

Enzyme Secretion

• Chief cells create pepsinogen to pepsin (active) & gastric lipase
• Paracrine Secretions: --D cells secrete both somatostatin (inhibits gastric acid secretion to prevent excessive acidity) and histamine -- Intrinsic factor is secreted to absorb Vit. B-12 and to bring it into bloodstream to marrow for RBC formation
  • Mucosal Cell is Responsible for creating an additional lining of resistance of denaturing from hydrochloric acid and Prevents auto-digestion of the stomach

Motility Control

• Intestinal Phase has a low rate to slow down and to regulate
• Its completed with digestive process which happens in the small intestine that leads to segmentation and peristalsis
• Maximation of surface area happens with: --Villi and ctrypts and a brush borders that increase ->Absorption, Hepatic Portal System , and the circulation in the liver of the Fats which uses lymphatic circulation