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  Phrasal verbs are meaning groups made up of a single verb and a particle (usually an adverb). A phrasal verb is a combination which takes on a new meaning independent of the original meaning of the verb: We ran out of the house. (The meaning of the verb does not change and out of refers to the house.) We ran into Mark on Saturday. (The meaning has changed. ➝ run + into means ‘meet’) Phrasal verbs are frequently used in English. They tend to be used in less formal contexts than single verbs: We need to sort out the problem. (less formal) We need to resolve the problem. (more formal) Phrasal verbs do not always have a single verb equivalent (resolve = sort out) , but whenever they do, we choose the single verb over the phrasal verbs in formal English, and the phrasal verb over the single verb in neutral and informal contexts. Transitive and intransitive phrasal verbs Phrasal verbs can be transitive (used with an object) or intransitive (used without an object): It’s cold, put your jacket on. (your jacket = object, put on is a transitive phrasal verb) The policeman let him off with a fi ne. (him = object, let off is a transitive phrasal verb) The realisation of the disaster slowly began to sink in. (no object, sink in is an intransitive phrasal verb) I’m sure the price of some vegetables will go down. (no object, go down is an intransitive phrasal verb) Some phrasal verbs can be both transitive and intransitive: Cheer up! I’m sure everything will be all right in the end. (intransitive) My best friend always knows how to cheer me up when I am upset. (transitive) Sometimes the same verb can be used transitively and intransitively, but with a difference in meaning: It took years to pay off the loan. (= give the money back, transitive) In the end, eating carefully and avoiding fatty foods paid off. (= produce good results, intransitive). We do not place an adverb or a passive object between the verb and the particle: She backed up their ideas forcefully. (NOT She backed forcefully up their ideas.) The plan for the food festival was put forward by the promoters. (NOT The plan for the food festival was put by the promoters forward.) Some examples of transitive separable verbs are: let down, lay off, back up, bring up, pay off, blow up, call off, turn on, turn off. In inseparable phrasal verbs, the verb and the particle are never separated: the object always comes after the particle: As delicious as pancakes are, you can’t live on pancakes alone. (the object pancakes comes after the particle) As delicious as pancakes are, you can’t live on them alone. (the object them comes after the particle) Some examples of transitive inseparable verbs are: look for, look into, break into, call for, fall for, get over, go through. Three-word phrasal verbs Three-word phrasal verbs are made up of a verb + adverb particle + preposition, and are also known as phrasal prepositional verbs. They are transitive (used with an object) and inseparable. The object always follows the fi nal preposition: He put up with the pain for as long as he could but fi nally asked for a painkiller. (the object the pain comes after the f i nal preposition with) A modifying adverb can only be placed between the adverbial particle and the preposition: He put up bravely with the pain for as long as he could, but f i nally asked for a painkiller. OR He put up with the pain bravely for as long as he could, but f i nally asked for a painkiller. Common examples of three-word phrasal verbs are: back out of, catch up on, catch up with, drop in on, face up to, get down to, look down on, make away with, stand up for

 

 

The Endocrine and Reproductive Systems

The Endocrine System

Recall that the nervous system involves the brain controlling and coordinating the body by sending electrical signals along neurons to various parts of the body. Similarly, the endocrine system controls body function as well. The endocrine system releases chemical messengers, called hormones, directly into the bloodstream.

Hormones and Glands

The endocrine system relies on hormones to function. Hormones are molecules that carry messages to other parts of the body. Hormones have specific shapes and other features so that they bind to specific receptors on or inside target cells. While both hormones and nerve impulses carry messages, hormones work more slowly than nerve impulses.

Glands are specialized structures in the body that make and release secretions, including hormones. Glands can be divided into two major groups. Exocrine glands release their secretions directly to the target organ or tissue and have specific ducts for their secretions. Sweat, tears, and digestive juices are all examples of exocrine secretions. Endocrine glands release their secretions, hormones, directly into the bloodstream. Once hormones are in the bloodstream, they are transported to target cells throughout the body. The major endocrine glands and their functions are shown in this table.

Endocrine Gland Function
Hypothalamus Regulates the functions of the pituitary gland
Pituitary gland Plays a role in many different processes including growth, puberty, and reproduction
Pineal gland Melatonin production and sleep regulation
Thyroid gland Regulates metabolism, body temperature, and calcium levels
Parathyroid gland Regulates calcium, magnesium, and phosphate levels
Thymus Helps the immune system develop
Pancreas Controls blood sugar levels
Adrenal glands Produces epinephrine (adrenaline) and norepinephrine, controlling the “fight or flight” response
Testes Develop male sex characteristics
Ovaries Develop female sex characteristics

You have encountered the term epinephrine before. Remember, when epinephrine is released from nerve cells, it functions as a neurotransmitter. However, when it's secreted by the adrenal glands, it's part of the endocrine system.

The hormones produced in a certain location travel elsewhere and affect other parts of the body. In addition to these glands, hormones can also be produced by bones, the heart, the small intestine, and fat tissue. Most cells can produce prostaglandins, hormone-like substances that have effects in inflammation and reproduction. When the body is injured, some prostaglandins affect mast cells, part of the immune system you will learn about later. These prostaglandins regulate the immune response, including swelling.

Hormone Action

Hormones can be classified as steroids or nonsteroids. Steroid hormones are made from cholesterol, so they are lipid-soluble. They can cross the cell membranes of target cells and bind to receptors to form a complex that enters the cell's nucleus. Once inside the cell nucleus, these complexes influence gene expression.

An image of a cell showing how steroid hormones enter the cell, then the nucleus to influence gene expression.The image above shows the process of how steroid hormones influence cell activity.

Steroid hormones enter the nucleus and affect the mRNA sequences produced by DNA, inherently changing gene expression. These hormones influence which proteins are produced by the cell, depending on what the body needs.

Review the following steps for how steroid hormones affect cell activity:

  1. The steroid hormone crosses the cell membrane and enters the cytoplasm.
  2. The steroid attaches to a receptor in the cell to form a complex.
  3. The steroid-receptor complex enters the nucleus and interacts with the DNA.
  4. A new mRNA strand is made to direct cell activity.
  5. The mRNA strand is translated into new proteins.

Nonsteroid hormones are proteins, peptides, and modified amino acids. Because they are not fat-soluble, these hormones do not enter the inside of the cell. Instead, they bind to receptors on the cell membrane. This binding triggers a cascade of events inside the cell; it activates enzymes and releases secondary messengers that influence specific cellular activities. One important secondary messenger is the molecule cyclic AMP (cAMP). When cAMP receives a hormone signal from the outside of the cell, it triggers a wide range of cell actions. When the hormone binds to its receptor on the outside of the cell, its message is relayed to cAMP by activating an enzyme. Then, cAMP carries the message into the cell, triggering further chemical reactions and activating other messenger molecules.

An image of a cell showing how nonsteroidal hormones bind receptors on the outside of a cell to influence its actions and do not enter the cell or nucleus.

Watch "Steroidal and Non-Steroidal Hormones" for a simple review of the main difference between steroid and nonsteroid hormones.

Role of Feedback

Endocrine glands are controlled by feedback mechanisms. Recall that feedback mechanisms occur when an organ responds to specific conditions, such as blood sugar concentration influencing whether the pancreas produces insulin or glucagon. Generally, a person only needs certain amounts of secreted hormones to function. When hormone levels are high, the gland producing that hormone responds to that feedback and stops secreting that hormone. When hormone levels in the body are low, the gland producing that hormone increases production, in an effort to maintain homeostasis. Water balance is another example of a feedback mechanism; the hypothalamus and posterior pituitary gland produce and release a hormone that maintains this homeostasis.


 

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