[RAP0 21LAB] PRELIM: Lesson 3 (Smooth Muscle Cell)

Smooth Muscle Cell

• It is a type of involuntary, non-striated muscle cell found in various organs and structures throughout the body.

• It plays a critical role in functions such as digestion, blood flow regulation, and respiration.

5 Characteristics of Smooth Muscle Cell

• Shape

• Nucleus

• Striations

• Control

• Regeneration

Shape

• Characteristics of Smooth Muscle Cell

• Spindle-shaped (elongated, tapered at both ends)

Nucleus

• Characteristics of Smooth Muscle Cell

• Single, centrally located ___

Striations

• Characteristics of Smooth Muscle Cell

• Absent (unlike skeletal and cardiac muscle)

Control

• Characteristics of Smooth Muscle Cell

• Involuntary (regulated by the autonomic nervous system, hormones, and local signals)

Regeneration

• Characteristics of Smooth Muscle Cell

• Capable of ___ through mitosis, unlike skeletal and cardiac muscle

6 Location of Smooth Muscle Cells

Smooth muscle cells are found in the walls of hollow organs and structures, including:

• Digestive System

• Respiratory System

• Circulatory System

• Urinary System

• Reproductive System

• Eye

Digestive System

• Location of Smooth Muscle Cells

• Stomach, intestines (controls peristalsis)

Respiratory System

• Location of Smooth Muscle Cells

• Bronchi, bronchioles (regulates airway diameter)

Circulatory System

• Location of Smooth Muscle Cells

• Blood vessel walls (controls blood pressure and flow)

Urinary System

• Location of Smooth Muscle Cells

• Bladder, ureters (aids in urine transport)

Reproductive System

• Location of Smooth Muscle Cells

• Uterus, vas deferens (facilitates childbirth and sperm transport)

Eye

• Location of Smooth Muscle Cells

• Iris and ciliary muscles (controls pupil size and lens shape)

5 Structure and Components of Smooth Muscle Cells

• Sarcoplasm

• Sarcolemma

• Actin and Myosin Filaments

• Dense Bodies

• Caveolae

Sarcoplasm

• Structure and Components of Smooth Muscle Cells

• The cytoplasm of smooth muscle cells, containing contractile proteins.

Sarcolemma

• Structure and Components of Smooth Muscle Cells

• The plasma membrane that helps in transmitting contraction signals

Actin and Myosin Filaments

• Structure and Components of Smooth Muscle Cells

• These proteins slide past each other to cause contraction, but unlike skeletal muscle, they are not arranged in sarcomeres.

Dense Bodies

• Structure and Components of Smooth Muscle Cells

• Protein-rich structures that serve as anchoring points for actin filaments (analogous to Z-discs in striated muscle).

Caveolae

• Structure and Components of Smooth Muscle Cells

• Small invaginations in the cell membrane that help regulate calcium ion influx.

Function and Mechanism of Contraction of Smooth Muscle

• Smooth muscle contraction is slower but sustained compared to skeletal and cardiac muscle.

• It occurs through the sliding filament mechanism, regulated by calcium ions (Ca²⁺) but with a different process

5 Function and Mechanism of Contraction of Smooth Muscle

• Calcium influx

• Calcium binds to calmodulin

• Calmodulin activates myosin light-chain kinase (MLCK)

• Myosin interacts with actin

• Relaxation occurs

Calcium influx

• Function and Mechanism of Contraction of Smooth Muscle

• It occurs through channels in the sarcolemma.

Calcium binds to calmodulin

• Function and Mechanism of Contraction of Smooth Muscle

• It happens instead of troponin as in skeletal muscle.

Calmodulin activates myosin light-chain kinase (MLCK)

• Function and Mechanism of Contraction of Smooth Muscle

• This happens leading to phosphorylation of myosin.

Myosin interacts with actin

• Function and Mechanism of Contraction of Smooth Muscle

• This happens, causing contraction

Relaxation occurs

• Function and Mechanism of Contraction of Smooth Muscle

• It occurs when calcium levels decrease, and myosin is dephosphorylated.

Single-unit (Visceral) and Multi-unit Smooth Muscle

2 Types of Smooth Muscle

Single-unit (Visceral) Smooth Muscle

• Types of Smooth Muscle

• Found in most organs (e.g., intestines, uterus, blood vessels)

• Cells are connected by gap junctions (allowing synchronized contraction)

• Functions as a unit (contracts together)

Multi-unit Smooth Muscle

• Types of Smooth Muscle

• Found in areas like the iris, arrector pili muscles, and large arteries

• Each cell acts independently, requiring individual nerve stimulation

• Allows fine control (e.g., pupil size regulation)

involuntary

Smooth muscle is ___.

4 Controllers of Smooth Muscles

• Autonomic Nervous System (ANS) Sympathetic system

• Parasympathetic system

• Hormones

• Local Factors

Autonomic Nervous System (ANS)

• Controllers of Smooth Muscles

• Sympathetic system

• Usually causes relaxation (except in blood vessels)

Parasympathetic system

• Controllers of Smooth Muscles

• Usually stimulates contraction (e.g., digestion)

Hormones

• Controllers of Smooth Muscles

• (e.g., oxytocin stimulates uterine contractions, epinephrine affects blood vessels)

Local Factors

• Controllers of Smooth Muscles

• (e.g., oxygen, pH, stretch response)

4 Clinical Relevance of Smooth Muscles

• Asthma

• Hypertension (High Blood Pressure)

• Irritable Bowel Syndrome (IBS)

• Uterine Contractions

Asthma

• Clinical Relevance

• Smooth muscle constriction in the airways causes breathing difficulties.

Hypertension (High Blood Pressure)

• Clinical Relevance

• Overactive smooth muscle in blood vessels increases resistance.

Irritable Bowel Syndrome (IBS)

• Clinical Relevance

• Abnormal smooth muscle contractions in the intestines.

Uterine Contractions

• Clinical Relevance

• Regulated by hormones like oxytocin (important in childbirth).