Respiration

Path of blood

1. Right atrium receives oxygen poor blood from vena
   cavae

2. Blood is pumped from right atrium to right ventricle

3. Right ventricle pumps blood to pulmonary arteries

4. oxygenated at lungs

5. Pulmonary veins return oxygenated blood to left
   atrium

6. Blood flows from left atrium to left ventricle

7. Delivered to body tissues

8. Veins (ultimately vena cavae) return blood to right
   atrium

Gas

substance with no fixed shape or volume, and widely separated particles, that expands to fill a “container”

Gas Exchange:

• Needed because of cellular respiration: O2 consumed and CO2 produced as byproduct

• Molecular mechanism of exchange: diffusion

• Molecules of each type of gas in mixture diffuse from region of higher partial pressure to lower partial pressure

Cellular Respiration

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O

Four attributes for effective respiration:

1. Gas exchange region must be moist: moisture allows gases to become/stay dissolved as they cross the gas exchange region

2. Gas exchange region must be thin: diffusion works best over short distances

3. Gas exchange region must have a large surface area

4. Concentration gradient must occur between the regions where gas diffuses (moves from high to low)

Lungs are the main organs of the respiratory system

• Lungs: exchange gases between environment and
  body

• Take in O2 from air and release CO2 into it

• Adults average 12-20 breaths per minute

• Left lung is slightly smaller to accommodate heart

Path of airflow

Nose/mouth → pharynx → larynx → trachea (“windpipe”) → bronchi → bronchioles → alveoli

“Air conditioning” along the path of airflow:

• nasal hairs: filters/trap out large particulate debris

• nasal cavity warms and humidifies the air

• air is sampled for odors

• mucus surfaces capture fine particulates

Alveoli

• tiny air sacs, surrounding capillary beds are ideally adapted for gas exchange

• very high surfaces in direct physical contact with capillaries and the environment

• one cell layer thick

• O₂ diffuses into the blood across alveoli

• CO₂ diffuses out of the blood across alveoli

• Surfactant: lipid and protein mixture preventing alveoli epithelium from sticking together

Breathing

• the alternate inhalation and exhalation of air (aka ventilation)

• diaphragm and intercostal (between ribs) muscles move lungs

• Inhalation: Diaphragm/intercostals contract and expand/lower – volume increase sucks air into lungs

• Exhalation: diaphragm/intercostals relax– volume decrease pushes air out of lungs

Important lung volumes

• total capacity ~5-6L

• tidal volume

• vital capacity

• residual volume

Tidal volume

• volume of air inhaled/exhaled in one normal breath

  • Resting Tidal Volume ∼ 500 mL

Vital capacity

maximum volume one can inhale/exhale in one maximum breath (typically 3 - 5 L)

Residual volume

(20 – 50% of lung volume) remains in the trachea, bronchi, bronchioles, and alveoli

Collapsed lung (pneumothorax)

Air (or fluid) gets into the area between the lung and chest wall and lung can not fill with air

The diaphragm contracts and moves downward during?

Inhalation

What is the primary stimulus causing breathing rate to increase during exercise?

Increasing level of CO₂

Regulation of breathing

• Rising CO2 levels decrease blood pH levels

• Body cannot tolerate much

• Sensors in blood vessels; brain detects drop in pH

• Brain signals rib muscles and diaphragm to increase breathing rate and depth

Human circulatory system connection

• The human heart is two pumps in one with two separate circuits:

  • The right side pumps oxygen-poor blood (blue)to the lungs

  • Pulmonary circuit: To and from lungs

  • The left side pumps oxygen-rich blood (red) to body tissues

  • Systemic circuit: To and from body tissues

• Oxygen and carbon dioxide are transported in the
  blood

Blood and its contents

• Blood

• Plasma

• red blood cells

• white blood cells

• platelets

Blood

involved in transport, immune defense, and temperature regulation

Plasma

Liquid part of blood

Red blood cells

AKA erythrocytes, transport oxygen

White blood cells

AKA leukocytes, resist infections

Platelets

repair damaged blood vessels

Hemoglobin

• has 4 heme groups, each containing an iron atom that binds one O2 molecule

• ~250-300 million hemoglobin per red
  blood cell

• Oxygen diffuses across the alveolus and into the blood plasma, then into red blood cells where it binds to hemoglobin

Hemoglobin binds and releases oxygen

• The partial pressure of O2 (Po2) is the relative amount of O2 available. O2 moves from high to low

• In the lungs (high Po2), hemoglobin will “pick up” O2; in the tissues far away from lungs the (low Po2), hemoglobin will release O2.

• Partial pressure gradient of O2 in body tissues determines how much is “unloaded from” hemoglobin

• O2 released rapidly during exercise as it is used quickly

The human fetus exchanges gases with the mother’s blood

• Fetal gas exchange occurs in the placenta; blood supplies do not directly mix

• Fetal hemoglobin has a higher affinity for O2 than maternal hemoglobin

• Fetal hemoglobin binds oxygen as maternal hemoglobin releases it

• Smoking during pregnancy reduces the supply of oxygen to the fetus by up to 25%

How many O₂ molecules can each hemoglobin carry?

4