BIOLOGY OF HUMAN AGING

Chapter 11

The Respiratory System

Outline• Review of the Structure and Function• Nasal Cavity, Pharynx, Trachea, Bronchi, Alveoli, Lungs

• Age-Related Changes• Trachea and Bronchi, Alveoli, Lungs Structural Changes

• Age-Related Dysfunctions• Chronic Obstructive Pulmonary Disease

– Emphysema

– Chronic Bronchitis

• Pneumonia

• Tuberculosis

• Pulmonary Embolism

Human Respiratory System

Functions: – Works closely with circulatory system, exchanging

gases between air and blood:• Takes up oxygen from air and supplies it to blood (for

cellular respiration).

• Removal and disposal of carbon dioxide from blood (waste product from cellular respiration).

Homeostatic Role:– Regulates blood oxygen and carbon dioxide levels.

Human Respiratory SystemComponents:

Nasal cavity, throat (pharynx), larynx (voice box), trachea, bronchi, alveoli, and lungs.

Pathway of Inhaled Air: Nasal cavity Pharynx (Throat) Larynx (Voice Box) Trachea (Windpipe)

Bronchi Bronchioles Alveoli (Site of gas exchange)

Exhaled air follows reverse pathway.

Human Respiratory System

Pressure Relationships

Figure 22.12

Blood Transports Gases Between Lungs & Tissues

Human Respiratory System1. Nasal cavity: Air enters nostrils, is filtered by hairs,

warmed, humidified, and sampled for odors as it flows through a maze of spaces.

2. Pharynx (Throat): Intersection where pathway for air and food cross. Most of the time, the pathway for air is open, except when we swallow.

3. Larynx (Voice Box): Reinforced with cartilage. Contains vocal cords, which allow us to make sounds by voluntarily tensing muscles.

– More prominent in males (Adam’s apple).

Human Respiratory System4. Trachea (Windpipe): Rings of cartilage maintain shape of

trachea, to prevent it from closing. Forks into two bronchi.

5. Bronchi (sing. Bronchus): Each bronchus leads into a lung and branches into smaller and smaller bronchioles, resembling an inverted tree.

6. Bronchioles: Fine tubes that allow passage of air. Muscle layer

constricts bronchioles. Epithelium of bronchioles is covered with cilia and mucus.– Mucus traps dust and other particles.

Human Respiratory SystemAlveoli (Sing. Alveolus): Grapelike clusters of tiny air sacs

with very thin elastic walls through which gas exchange occurs.– Oxygen in air enters blood in capillaries.

– Carbon dioxide in blood enters air in alveoli.

There are several million alveoli in the human lungs, with a total surface roughly equivalent to a tennis court.

The walls of the alveoli are very delicate.

Alveolar macrophages are phagocytic cells that swallow inhaled particles (dust, bacteria, etc.) and digest them.

Exchange of Gases Occurs in Alveoli

Human Breathing: Inhalation and Exhalation

Lung volume and using spirometer

Lung volume and using spirometer

Age-related changes• Trachea and Bronchi

– Progressive calcification

– Smooth-muscle replaced by fibrous connective tissue

– Reduced elasticity of the lungs

– VC begin to decrease ~ 40 years of age

– Mucous membrane lining the trachea and bronchi

show degenerative changes

– Decrease activity of cilia and phagocytic activity of

the macrophages

Age-related changes

• Alveoli

– Gradual deterioration of the walls of alveoli

– The size increases but less surface area for the

gas exchange

– Cross-linkage

– More collagen fibers and less elastic fibers

– Declining oxygen levels in the blood

Age-related changes

• Lungs

– Lose their elastic recoiling capabilities and offer less

resistance to expansion

– Insufficient ventilation contributing to an overall

reduction in oxygen saturation of arterial blood.

– Surface area

– Diminished sensitivity of chemo-receptors that

monitor oxygen and CO2 levels in the blood.

Human Breathing is Automatically Controlled

Age-related changes

• Structural changes– Kyphosis and the hunching over reduces the volume

of the thoracic cavity and make it more difficult to expand the lungs

– Loss of Ca and weakening of muscles– Diminished elasticity and increases fibrosis of the

lungs– Stiffness of the rib cage– Older individual rely more on the diaphragm

Age-related dysfunctions

• Dysfunctions of respiratory system are more common in older individuals

• These are not merely a result of aging, rather due to constant exposure to environmental stimuli (air pollution & smoking)

• Air pollutants damage trachea, bronchi, alveoli

• Most frequently occurring pulmonary disorders:– Restrictive (hinder lung expansion)– Obstructive (involve respiratory airways increased

resistance to air flow

Chronic Obstructive Pulmonary Disease (COPD)• Characterized by chronic air flow obstruction in lungs

• Reduction in the ratio of forced expiratory volume in the first second to forced vital capacity (FEV1/FVC)

• Symptoms:

• Difficulty breathing, wheezing, cough, etc…

• Increase rapidly in >50 years of age, frequent in men

• Cause:

• Environmental factors and age (also genetic predisposition)

• 80% of cases is due to cigarette smoking

• Two most common types: Emphysema & Chronic bronchitis

Emphysema• Excessive air accumulates in lungs as they lose their ability to

ventilate properly

• More prevalent in older people

• Gradual development in response to smoking, bronchitis, pulmonary irritants

• Mechanism• Chronic irritation, smoking, infections paralyze & deteriorate

mucus membrane cilia excessive mucus production w/in airways to the lungs persistent cough

collapse of airways hinders air flow through lungs air becomes trapped in alveoli

• Trapped air alveoli remain inflated expiration (normally passive action) requires muscular resistance significant energy needed to exhale development of Barrel Chest

Over-inflated alveoli destroy alveoli’s wall replaced by fibrous

tissue hinder gaseous exchange

Early stages: gaseous exchange fairly adequate no cyanosis

Later stages: great reduction in area where gas exchange occurs

cyanosis even w/ mild physical effort

Patients often have low maximum breathing capacity and high

residual air volume

The disease can not be reversed and gradually worsens

Therapy: positive-pressure oxygen therapy to force O2 into alveoli

Emphysema puts extra load on heart (attempts to pump more blood

into lungs to compensate for O2 deficiency)

Patients suffering from emphysema die from heart failure

Dirty lung of an Emphysema (smoking) patient

Bronchitis Acute or chronic inflammation of the bronchial tree

Caused by bacterial infection or by irritants (smoke in inhaled air)

Chronic bronchitis is due to long-term exposure to environmental

insults more common in elderly

Similar to emphysema airway irritation responds by mucus

production

In severe cases, mucus membrane becomes swollen and partially

obstruct airway severe hindrance of gas exchange cyanosis

Excess mucus buildup is removed by persistent coughing

Pneumonia Inflammation of the lower airways of the lungs

Symptoms: Fever, cough, sputum production (not restricted to older

individuals)

Classification (due to variability in causative agents):

Community acquired: viruses (influenza) or pneumococcus

Hospital acquired: gram negative bacilli (E. Coli) or Enterobacter

Aspiration pneumonia: inhalation of foods or foreign bodies that

obstruct bronchus

causes lung collapse, fluid accumulation, infection

More common in older (bedridden) individuals

Classification of Pneumonia

Tuberculosis Caused by mycobacterium tuberculosis ; enters body with inspired

air lung tuberculosis is the most common form

Symptoms: early (subtle) weight loss, fever, cough

Diagnosis: skin test, chest x-ray, sputum culture

Lung phagocytes destroy the bug alive bacteria are walled off in small or calcified nodules (Tubercle)

Evading bacteria spread lung tissue replaced by fibrous tissue reduced vital capacity and difficulty breathing

Antibiotics harnessed TB till mid-80s resurgence due to AIDS

Role of immune system in controlling outward signs of the disease

Dormancy impaired immune system Reactivation tuberculosis

Causative agent: mycobacterium tuberculosis

X-ray film of infected lung

Pulmonary Embolism Ambolus: blood clot or foreign objects that flows freely w/in blood

vessels

Can reach vessels with small diameter, can not pass through them partial or complete block reduced blood flow to the tissue tissue dies

Pulmonary embolism: a clot that blocks a branch of pulmonary artery

Symptoms: shortness of breath, chest pain, spitting blood, accelerated heart beat and breathing rate, anxiety

Can occur at any age, more common in bedridden older individuals

Immobile patients tend to develop clots in leg veins (low blood flow)

Treatment: – Anticoagulant drugs (streptokinase)